Have you been VAC'd? Not to fear! This guide will help you play the latest MW2 patch (1.0.182) without worrying about VAC.
(This is basically a VAC bypass for the 182 version of the game. This does NOT work with pirated versions of the game.)
Firstly, you need to have the newest version of MW2 installed.
Second, get the Zero Gear Demo on Steam (Zero Gear Demo on Steam) (<--- I can't upload that to MPGH, duh xD)
Once the ZG demo is fully installed, delete everything from the Server folder (C:\Program Files\Steam\steamapps\common\zero gear demo\Server). (Not the folder, just the files)
Copy and paste (or move) everything from the MW2 install directory (Found in C:\Program Files\Steam\steamapps\common\call of duty modern warfare 2) to the Sever folder inside the Zero Gear Demo folder.
After you have done that, edit the ZeroGear.bat file (Right click, edit) in the main ZG demo folder so it say's: "cd Server
START iw4mp.exe" (Without the quotes), then save and exit.
Run Zero Gear Demo from the My Games list in Steam. If you have done everything correctly, it should launch MW2 instead of Zero Gear Demo.
Happy hacking!
PS: I figured this out after I was VAC'd yesterday, and this also works with accounts that are not banned.