Future pricing for Win 7 and Plans for New OS

Based on the history of past windows OS's, is it possible to estimate how much cheaper the full versions of Windows 7 would be after a year? Specifically the professional or ultimate versions?

I'm using XP Pro and I'm very comfortable with it and don't feel like I need a new OS just because it's new and has the latest bells and whistles. My 2 factors for deciding to upgrade depend on price and future OS plans from Microsoft.

For price considerations, I can get the full version of Win 7 Professional for $100. Should I wait to upgrade to Win 7 professional to see if prices will get better, or is this already a price that even waiting won't beat?

As for future OS's, is it worth it to get 7 if Microsoft is going to come out with a new one in several years? How long do you think 7 is going to last? XP's had a very long lifespan, so if it's going to be anything like that, I would consider upgrading. But if not, maybe I can hold on to XP for a few more years for the next OS.

Given these 2 factors, any recommendations?

I believe the best deals tend to be available around launch time (or before). Things like the family packs are expected to go away.

You might find a better deal if you qualify as a student in the future or something like that, but otherwise you're unlikely to beat your $100 Professional thing down the line. Things should largely remain at full list price indefinitely. They don't really have inventory with a limited life they have to clear out or anything like that. I suppose you may find a better deal by the time Windows 10 rolls around and Windows 7 doesn't qualify for upgrading, etc., but that's a long ways off.

I would not plan to hang onto XP for "a few more years." I'd expect it to be less and less supported.

One big consideration is if you might buy a replacement computer in the near future though that would come with Windows 7 preinstalled. If so, buying a separate upgrade now could be a waste.