Go to your AvP directory and find the folder "Profiles", in the "Profiles"
folder you will find a text ".txt" file with your player name/s.

Open your player text ".txt" file and scroll down till you find the caracter 
name such as "[Alien]",  under each name you will see the the following:

"LevelStatus = (DWORD)284646098", now where the bunch off numbers are just 
replace them with the folowing numbers, each caracter 
has diferent numbers, so do like so:

[Alien]
LevelStatus = (DWORD)2846460546

[Marine]
LevelStatus = (DWORD)2846460556

[Predator]
LevelStatus = (DWORD)2846460576

HEHE, now all ur levels are unlocked, OK! I gave my end of the deal,