Most popular DOS games now have Windows Ports. Some examples being, Doom and Duke Nukem 3D, Rise of the triad, Commander Keen, and Quake.
For other games, you can use something like DOSBox, which is pretty much a DOS Emulator.
Some folks will stop me here, and say "But I don't want to emulate DOS to play DOS games".
Well, if that's the case, you can't really use XP either. XP, like any NT-based Windows OS, runs DOS programs using virtualization. DOSBox is just a much better approximation and is built to different standards- NTVDM (the DOS Emulator XP and 32-bit Vista and 7 uses) is built for compatibility with boring old business DOS programs. DOSBox is built for compatibility with DOS Games. Because DOSBox is a software emulator rather than a virtualizer, it also works on 64-bit Windows.Not to mention allowing a wider variety of games and programs to work successfully on XP.
Add in the fact that XP support is being dropped and it's 13 years old and you are setting yourself up for problems from both fronts. Newer games will not run as well on a 32-bit platform, and DOS compatibility is mediocre at best, almost entirely because of our current hardware. DOS games under XP will be virtualized which means they will be talking to your hardware, in a manner of speaking. The problem being that modern graphics cards aren't exactly tested to see how well they wrun in 640x480 with 256 colours or other lower resolution graphics modes that games use.Some simply don't work at all with those video modes or display garbled screens. Since DOSBox is a full software emulator, there is no virtualization, the game will interact with the devices the emulator uses Windows Graphics capabilities (OpenGL and Direct3D) to display what is happening. So even if your latest and greatest graphics card doesn't work with VGA's undocumented 320x240 Video mode that is used by some games, DOSBox does work with it.