Nearly all 32-bit software will work on 64-bit OS/hardware no problem. I'm running Windows XP 64-bit right now. Software is not an issue until it involved hardware tie ins. I currently have everything working properly but some hacks were involved to get it all going.
I played StarCraft and Age of Empires II on 64-bit Windows 7 Ultimate. There were some graphical issues with AoE II but it worked.
So my impression of Windows 7 64-bit will be that, the software will work but some graphic problems may occur. This shouldn't be architecture related.