In 2006, Microsoft released Vista. This new operating system was sadly not compatible with the Game Theater XP's drivers and a statement was issued that there was to be no support.
Apparently, however, Hercules was awesome enough to release a new set of drivers for the card which (supposedly) enable Vista support.
So if you own one of these cards and can't use it due to Vista, rejoice and download. This is almost a year-old news but I figured somebody out there might appreciate it.