Ooh. Here's a bit of an "oops" for Microsoft: It turns out it's possible, with no hacking or advanced skills required, to make a full-blown clean install of Windows Vista from a Vista upgrade DVD. Seeing as the upgrade disc costs about two thirds what the full version does, that seems like a pretty big oversight. DailyTech has the scoop. The process is very easy, but takes a bit of legwork. Here's the basics:

1. Boot from your Vista upgrade DVD.
2. Don't enter your product key when prompted; click "Next" instead, which will install a 30-day trial version of Vista.
3. Once your new trial boots up, launch setup from the DVD again, from within Vista.
4. Enter your product key when prompted, and then choose Custom (advanced) to do a clean install (yes, you're installing Vista a second time).
5. Congratulations, you've got Vista!

According to Paul Thurrott, all of this info is actually contained within internal Microsoft docs, so it's kind of amazing to me that Microsoft shipped Vista update discs with this capability. Regardless, doing this is almost certainly in violation of your license agreement, so don't try it at home (but if you do, let us know if it works).