The only issues you are likely to encounter with Win 7 64 (or Vista 64) are...
1) Ancient games that use 16bit, DOS, etc. will not run natively.
2) Modern games that use copy protection and do not have updated DRM driver support.
For (1), use an emulator, most of these games ran on machines slow enough to be emulated in software if hardware support is not possible.
For (2), you may be flat out of luck, but these games are rare.
You could also use a second drive / partition and dual boot for some classic game that you really must play.
Check the compatibility lists that are available, like: http://www.overclockers.com.au/wiki/...atibility_List