It only supports vista SP2(?) and up at the moment.
XP doesn't support DirectX 10, unfortunately. I make use of many D3D10 features to optimize the application, as well as capturing. It allows me to do more things via the GPU directly rather than have to use the CPU and slow things down. I also use the latest visa/7 audio subsystem for audio capture.
I really wish I could support XP, but unfortunately I just can't. Microsoft in their greedy wisdom denies technology advancements in older versions of windows in order to force people to upgrade -- and it sadly works. I'm not going to lie, I do not like microsoft at all. They should have been split up in the 90s, but then the law for splitting up companies to prevent monopolies mysteriously seemed to vanish (got to love corrupt lawmakers).
In my ideal world, everyone uses linux, and free knowledge is encouraged to help further develop technological advancement. But sadly money is all people seem to care about, and if there's one thing microsoft has, it's money.