If you cannot simply reinstall Windows XP, Windows 7 Professional and Ultimate can run Windows XP mode, which is a virtualization tool that may give you the ability to run old XP-compatible software in a window under Windows 7.
Personally, I would not have upgraded. If I’m making money doing video, I do everything I can to make sure that I have a good installation of anything that makes video. I don’t let my Mac automatically update, I don’t update Quicktime Pro and I never update the boot drive with new system software unless I have a clone of my old system.
Same with PCs. I used the Avid DS with a PC and we never upgraded Windows XP to anything. When Service Pack 3 came out, we waited until Avid had released a patch that would prevent SP 3 from borking our systems. When Avid released version 8, which ran on XP-64, we were never tempted in the least to try Vista. Current Avid editing software that runs on Windows runs on Windows XP or SP-64 — they have not transitioned to Vista or 7.
I realize Adobe applications tend to keep up with OS changes better than Avid’s highly proprietary stuff, but I would seriously hesitate to install Windows 7 on any machine that is used for production, until or unless Adobe released a version (or an update) specifically for the new OS. And it is highly unlikely that CS3, Premiere Pro 2 or the version I use, 1.5, will be updated to work with Vista or Windows 7.
What if there were no hypothetical questions?