First off, good luck. 🙂
If you’re wanting to put Vista on a machine that’s already running XP, don’t wipe out XP altogether. Instead, run through the Vista installation and place it on a different drive and/or partition (which can be dynamically created during the install process). You may not like Vista, or you’re likely to find that your software just doesn’t work like it does in XP. At least you can go back to using XP if Vista doesn’t work for you.
Start emailing your favorite software authors now – if they’re still actively developing your favorite applications. With any luck, they will release a new version if Vista incompatibilities exist. However, I’d ask ’em today rather than waiting to find out later that the software doesn’t work correctly. Consider this a friendly reminder.
If you want to view PDFs, you’re going to need help installing Adobe Acrobat Reader 8 on Vista (as Adobe’s current installer chokes on its own spittle).
If you have a Smartphone or Pocket PC device, you’re going to need to download Windows Mobile Device Center instead of using ActiveSync. I’d imagine that by the time Vista officially hits the streets, this will be passed through Windows Update automatically.
And there are a thousand other things that I haven’t figured out yet.