Hi,
As you know protools 9 is qualified on PC for Windows 7.
I've tried it on XP and it work with ASIO. But carefull when you want to use Avid/digidesign audio drivers. The new ones compataible with protools 9 are only compatible with Windows 7.
Also the migration from windows XP to Windows 7 has to be done manually and you need to reinstall all the programs.
Hope it helps.
Proaudio-plugins.com