Left 4 dead will work with Windows 7 32 or 64 bit. I think the Godfather 2 might only work with 32 bit. I've seen Call of Duty 4 work on 64 bit, so it should also work on 32bit Windows 7.
Do you already have the games, or are you planning on buying them? I don't think you can buy Godfather 2 on Steam, but L4D and COD4 are pretty cheap if you buy them through Steam. I'm pretty sure a lot of their games don't have DRM. I remember I bought Half-Life 2 through Steam Store years ago, and if you make 1 account, as long as no-one else is logged onto that account, you can have it installed on as many computers as you want. Plus Steam is one of the cheapest, if not, is the cheapest place to buy games.
Also if you have a Win7 64bit system, and the game only runs on 32bit OS, you could try using compatibility mode. Just right click on the game icon,select properties, click on the compatibility tab, then enable compatibility mode.
for call of duty 4 you may have to go to punkbusters website and update it manually (follow the instructions there. Otherwise servers will constantly kick you off.
all games work on 64-bit or 32-bit systems bec. games are designed on a 32-bit processiong mode and any 32-bit program automatically works on the 64- bit system.
