64 bit will allow you to use more total memory (video card + memory modules), with the 32 bit OS your limited to 4GB total memory (Videocard + memory modules). A lot of the new games coming out will be written opitmally for 64 bit and there is may be limited features for 32 bit support. I can not give the names of the outcoming games (NDA's ftl), but a few of them are primarly written for 64 bit OS's and they have some limited features for 32 bit in terms of graphics level and UI functions.
The future of computers is in 64 bit OS's.