I recommend playing all Games on Semi-Pro to unlock those Achievements on your way to the 300 aswell :
The Winning streak. achievement in FIFA 07 worth 174 pointsHave a 60 game Winning Streak on Semi-Professional difficulty. The Goal Getter. achievement in FIFA 07 worth 99 pointsGet an average of 4 goals per game over 50 game on Semi-Professional difficulty. The Undefeated. achievement in FIFA 07 worth 81 pointsRemain undefeated for 50 games in Semi-Professional difficulty. The Fair Play Award. achievement in FIFA 07 worth 119 points20 Games without a card being shown in Semi - Professional difficulty.
Except the 20 Games with the World XI Team.
I was suprised as i unlocked the Achievement after Game 302.
So if it doesnt unlock at Game 300,keep playing and winning a few more Games.
You can either play Quick Play (recommend) or Manager Mode (dont Simulate,you have to play)
If you have problems winning or shooting much Goals,you can Destroy some Teams Statics.
Its a bit time consuming,because you have to edit each Players Attributes to 1.
A prove of my own Stats :http://imageshack.us/photo/my-images/267/bild0037jou1.jpg/