not answering the question, but i would personally recommend upgrading anyway. it proved a better OS for me. And the general thought is that the next version of protools will be 64 bit, so you will have to upgrade to take full advantage of that anyway. XP will become obsolete eventually, as with everything!
PT9 will not install on anything but Windows 7, so I can't imagine why PT10 would.
If you happen to be a student, you can get Win7 for $30 from Microsoft. If not, the price isn't too bad, considering how much previous Windows releases used to be.