All Levels
Create a new directory with "Profile0" name in your "c:Program FilesCodemastersPerimeterResourceSaves" directory.
Create a new file with text editor, called as "data" (without extension!) in your "Profile0" directory.
Just copy and paste the following lines into your "data" file:
[General]
name=ABBYCHEAT
lastMissionNumber=28
difficulty=1
Save your file. Now you have access to all missions in campaign/battle mode.