Virtual XP has a S3 video setup, It was not created to run any type of 3D games.
Its manly there to run old legacy app for business that cant get their apps re-written on newer OS due to cost or what every piece of equipment the software is written to run. You maybe able to get some old DOS games to run in it as for any type of Direct 3D games it will be a very slim picking another guess would be some old games made around 1995-98 any game that doesnt require direct 3d to run.
Some one down the line may fine a way to hack in something that will work, but I'm thinking that might be a long way off, since the Virtual XP will only be available to Enterprise and Ultimate Editions of Windows 7. By the time some get that to work GameGuard will have a fix out for Windows 7.