How to move Steam games on OS change (32-bit to 64-bit)

Solution 1:

All you need is Steam.exe and the steamapps folder. Move those into C:/Program Files (x86)/Steam and run Steam.exe. The application will redownload all of the steam files and will automatically detect all of your installed games in the steamapps folder. It's a really neat program actually.

As far as I know, Steam doesn't use 64-bit for the client or for the games, so you shouldn't run into any issues.

Solution 2:

For the past 4 years I've just moved the same Steam directory around to my other computers (or to a temporary drive when I do a reformat).

Occasionally you have to reinstall the Steam client over the old install, but this is, in my experiences, rare.

You should have absolutely no issues.

EDIT: Also remember that some of your save games get saved into your My Documents folder. Don't forget those if you want your old saves!