If you have an XP license not tied to particular computer, you can install it inside of VMWare or Virtualbox. Otherwise, get pro for the virtual PC (alternatively, if you're student or something, and can get XP much cheaper than the cost difference with pro, maybe do that?). Anybody can say you should be fine, but then they need to go try playing those games, and you might be surprised how many work, but what ones don't (Diablo FI, needs either a 32-bit install, or a virtual machine--I found other workarounds to not work). Some games from the mid/late 90s that were made for DOS-based Windows versions, and used 3D hardware, just plain need an older PC, at this point. As HW 3D virtualization support gets better, they might come to working, but some are still in a bit of a donut hole (FI, I can't get System Shock II to work in 7 64-bit, the patch for it floating around the 'net didn't work for me, and it needs 3D that it can't get in the VM).
You could also get a 32-bit Windows version, but then you're stuck with less RAM (3.2GB or less, depending on mobo and video card) for newer software, and some old software will be incompatible with Vista and 7 regardless of 32/64-bit.
Also, either way, make sure you get a CPU/chipset than has HW virtualization. Most do, but verify the chipset and CPU model support it, just in case. It will make the difference between the old 2D games being playable or not, in a virtual machine.
Try every game natively, then search for workarounds, then try them in a virtual.