You might also need some drivers from MS, although where they've hidden them I don't know, otherwise it will just be seen as a standard DirectInput controller, which Audiosurf doesn't support (which is why the Saitek P990 doesn't work).
I THINK they come with SP3 on XP, but I've not used XP as a gaming system in months and months so I can't remember.
Vista and Windows 7 come with the 360 drivers anyway.