64 bit is the future. Today's games are eating up memory like crazy as textures get larger and models get more detailed. For hyper-realistic games like Crysis, you're gonna need as much memory (both system and video) as you can spare.
Even games like GalCiv 2 and WoW are eating up memory like crazy as people keep demanding larger maps and longer draw distances. Huge worlds and large universes means lots of memory, even if it's not a game that pushes video cards to their limits!
The only major issue you'll encounter is if you plan on playing ancient DOS or Windows 3 games - but those can be played on a virtual machine or on an emulator. Truth be known, I started using DOSBox even in XP, as XP itself is missing 99% of what DOS games generally needed to run.
Yes, DOSBox should work. For Windows 3 games, Virtual PC should work.
In fact, Virtual PC is good for pretty much any game that really wants to use an older OS as long as the game doesn't require hardware 3D acceleration. Just be aware that virtual machines running Windows use a lot of memory and hard drive space.