Whats The Best Way To Go From Vits To XP?

What is the best way to go from Vista back to XP? Can I use an upgrade disk or must I purchase the full version for $270? The super-secret DRM file indiv02_64.key once again is crashing Media Center and everything else. I cannot watch TV, watch a DVD, or even watch Netflix online. I know from a previous encounter with MS support that I must wipe out the computer and reinstall. The only DRM content I watch is cable TV, Netflix online and DVDs from Netflix. How can this OS possibly be this fragile? I won't go into what an adventure it was to get Bluetooth to work.

The last time DRM crashed (4 months ago) I had to call MS support, pay $60 and spend 6 hours on the phone just to get a CD key for Vista Ultimate since a total reinstall apparently is the only option. I had done Upgrade Anytime and hence had no key - I instead had a license file which could not be accessed since the desktop was deactivated since I had no CD key. Said my support call charge would be refunded but of course that was a lie. Between the original purchase, upgrade purchase, support call to MS, and now possibly a full-version purchase of XP this will cost me close to $1,000. If MS products fail to function properly, I must pay more money to MS. That's getting old fast.