Definitely not a hard achievement as long as you can survive level one!
Right near the beginning, destroy the first 'falcon' emblem when it opens up and you'll receive the laser power up.
As you gain this power up, you'll see a first aid balloon come from behind you. Make sure you shoot this and you'll gain the spreader power up.
As you progress past the exploding bridge, you'll see the next 'falcon' emblem on the pipe next to the waterfall. This will give you the weapon which I can't even describe!
The last weapon is, again, hidden in a falcon emblem just behind the two big turret guns that appear out of the ground below the higher ground. This will give you the machine gun power up.
As long as you've gained all these power ups then that's achievement unlocked!