Your mileage may vary.
I have a unique boot system. It is not really a dual boot which is not unique, but instead, XP on one hard drive and Vista 32 Ultimate on another hard drive.
Recently, someone gave me a head's up that Amazon was selling pre order, Windows 7 upgrades from V 32 to W7 for 49.95.
I ordered it. Supposed to be released and out to me in October.
This is upgrade only, and Vista to W7, not XP to W7.
W7 will have to convince me to update my XP. I am so pleased with XP as most of us are.
I have Vista to learn it and play with it, and get the feel of it. (Insert smart remark here)
I can swap files between XP and Vista with ease so I can test and try all types of stuff.
Many times, the offer of a FREE upgrade is used to take away your hesitancy toward buying a computer today, or waiting for W7.
Just read the fine print! If I do get convinced that W7 is superior to XP, then I know I will need to buy the Full Install, and start from scratch installing stuff.
No one really likes that part of it.
Fred