S.S.D.D. 1/1: Modern Warfare 2 intel 1/45
In the very first tutorial mission, you can find one lone piece of intel. Once you've provided the gun training and thrown a grenade at the targets, before you go down the stairs to The Pit, turn around. Inside the tent in the opposite corner is the first piece of intel on a table.
Team Player 1/2: Modern Warfare 2 intel 2/45
Now you're into the proper missions, the second intel can be found inside the school on the mission Team Player. Play through the mission until your vehicle gets hit by an RPG, then you'll come across a school. Clear the ground floor, head up the stairs, then clear the enemies all shooting out of the windows. As you turn the corner, Sgt. Foley will say he saw one head into the classroom. The next piece of intel will be on a white table with a green chair on the right-hand side.
Team Player 2/2: Modern Warfare 2 intel 3/45
The third piece of intel is just a few steps away. Kill any remaining enemies, leave the school, and you'll see the laptop on a brown crate next to an ammo box.
Cliffhanger 1/3: Modern Warfare 2 intel 4/45
Play through the mission until you shoot the second pair of enemies in stealth and you split up with Captain MacTavish. Dead ahead, you'll be able to see a guard tower through the blizzard. Kill any enemies in the immediate area then climb the ladder to find the first piece of intel on the catwalk.
Cliffhanger 2/3: Modern Warfare 2 intel 5/45
After you place the C4 and MacTavish tells you to race him to the hangar, you can grab the next piece of intel. You're meant to meet him behind the first hangar on your left along the airstrip, but instead of going there, keep going past the second hangar then take an immediate left turn and go to the back of that hangar. Inside will be two engineers working on a vehicle. Shoot them both – don't worry, killing one won't alert the other – then smash the glass window with your melee attack to pick up the intel sat on a barrel.
Cliffhanger 3/3: Modern Warfare 2 intel 6/45
This one is a bit of a pain. Play until the section where yourself and MacTavish are on snowmobiles with enemies gunning for you from every direction. When you're given the on-screen prompt "press L2 to shoot" and MacTavish says "Don't slow down! Keep moving or you're dead!", you should be able to see a rickety wooden fence in front of you.
Make an immediate left turn at this fence and in front of you will be a cluster of trees, with paths either to the left or the right. Slowly drive into these trees – the objective marker should be approximately 1810m away at this point – and bear slightly to the right. You should be able to see the intel on the ground by the base of a tree. You don't need to hold down any button to pick it up, just drive over it.
There are no pieces of intel in No Russian, so you can play through this mission however you like.
Takedown 1/4: Modern Warfare 2 intel 7/45
Play through the opening sequence until you get to the point where you jump into the favela with Meat and Royce. Fight through the favela along the left-hand side until you reach a clearing with a Brazil flag hanging from one of the huts. Enter the hut to the right of this, with some football graffiti on the wall next to it, and the first piece of intel is on a table in the room at the back.
Takedown 2/4: Modern Warfare 2 intel 8/45
After you pass the fence with the rabid dog behind, clear the enemies and climb the stairs, then take a left. Fight through the enemies until the path forces you to take a U-turn. There should be another Brazil flag hanging from a balcony on your left-hand side, while in front of you there should be a ladder. Climb the ladder and the intel is on a table through the open door in front of you, provided you've killed the enemy inside.
Takedown 3/4: Modern Warfare 2 intel 9/45
Immediately after grabbing the second intel, head south-west (towards the objective) and there should be a brick building on your left. Go up the stairs to the door with the football graffiti to the side and the third intel is in the dining room on a small coffee table.
Takedown 4/4: Modern Warfare 2 intel 10/45
Keep fighting through the favela until you reach a section with a burning car blocking most of the path. Go past and enter the immediate door on your left. Walk down the stairs and the final piece of intel for this mission will be on a coffee table by the bed.
Wolverines 1/4: Modern Warfare 2 intel 11/45
Play until you reach the alley behind Joe's Diner, when some enemies jump out of a truck in the car park in front of you. Kill them all, followed by the ones inside the gas station next door, then enter the gas station to find the intel on the counter between the tills.
Wolverines 2/4: Modern Warfare 2 intel 12/45
Continue with the mission until you get the objective to secure Burger Town. Run over there, clear the enemies from inside, then head to the garbage disposal area to the left of the main entrance. Approach the big dumpster and you'll be able to see the next intel inside.
Wolverines 3/4: Modern Warfare 2 intel 13/45
Immediately afterwards, go east to Taco To-Go. Smash a window and climb through to find another intel on a table.
Wolverines 4/4: Modern Warfare 2 intel 14/45
Now run north, through Nate's and to the CRB bank on the other side. The final intel on this mission is left of Customer Service, under the Online Banking sign.
The Hornet's Nest
The Hornet's Nest 1/4: Modern Warfare 2 intel 15/45
After you've destroyed the two technicals in the first combat sequence, enter the house with the yellow wall and two barred windows, with the low cinderblock wall around the front. The first intel is on the kitchen table inside.
The Hornet's Nest 2/4: Modern Warfare 2 intel 16/45
After the flaming truck passes you, take a left turn and kill all the enemies in the clearing with the basketball hoop. Right before you go up the stairs at the other side, the next intel is behind the washing machine on a green barrel.
The Hornet's Nest 3/4: Modern Warfare 2 intel 17/45
Once you've cleared the intersection in the following combat area, you'll see Pelayo's ice cream shop on the right-hand side. Enter the building and go up the stairs, then take a right and go into the next building with some enemies in. Kill them all, then go up the following stairs in the yellow room with the cracked walls. You'll find the intel on a table upstairs.
The Hornet's Nest 4/4: Modern Warfare 2 intel 18/45
When Nikolai attempts to land but is pushed back to the second rendesvouz point, clear all the enemies around the football pitch, then walk behind the goal at the other end. The final intel is inside the window behind it.
Exodus 1/3: Modern Warfare 2 intel 19/45
Follow your squad through the houses until you reach the Garden Villas Apartment Complex. On the right-hand side of the driveway into the building is a security office; intel number one is on the table in the corner.
Exodus 2/3: Modern Warfare 2 intel 20/45
Fight up the street until you reach the Arcadia checkpoint. On the right-hand side, just past the large fountain, there's a security office. Head inside and turn around to find the intel next to the door on a table.
Exodus 3/3: Modern Warfare 2 intel 21/45
Cross the bridge into Arcadia and enter the second house on the right-hand side of the street. Go upstairs and the intel will be on a sofa on the landing.
The Only Easy Day... Was Yesterday
The Only Easy Day Was Yesterday 1/3: Modern Warfare 2 intel 22/45
When you've saved the first room of hostages and climbed the stairs to deck two, check the shelves against the wall on your left for the first intel.
edit*: If your achievement doesn't pop until 23, you will need to delete your save file after you get every other achievement in order to get the achievement for collecting 45 intel. I know it sucks, but unfortunately that's the only way.
This is my first guide ever. Let me know how I did. Hope I didn't miss anything and was accurate enough. Thanks You!
Side note: If anyone knows how to put pictures from my computer on to here that would be very helpful. I had pictures to go along with the steps from Activision, but was unable to add them.