Once Again: we are discussing upgrade methods and licenses here, not the fresh install & full license.
1. How to upgrade on top of installed OS
a. You cannot upgrade from 32-bit to 64-bit or vice versa.
b. You cannot upgrade between different languages, i.e. From French to English, or from Swahili to Tonga :)
c. You also cannot upgrade from XP. A slight twist though: you can upgrade from XP to Vista with SP1 and after that to Windows 7
d. To make stuff even more complex you have a strict matrix as of what editions can be upgraded with what:
*** 7 Home Prem 7 Prof 7 Ultim
Vista Home Basic + - +
Vista Home Prem + - +
Vista Business - + +
Vista Ultimate - - +
2. How to make a fresh install with upgrade license key?
a. Well actually you are right: there are now cheap upgrades for graduates or family packs, so you are one of those who would be very happy to install 64-bit Win7 and doesnt need her old 32-bit XP. But right at this moment you only had a 64-bit executable that wont run on this XP machine.
b. By the time this article is being composed, Microsoft already provided a download link for 64-version, and I hope for the 32-bit one there will be one soon. So I presume you all have already the bootable installation DVD in hand.
c. Simply boot from the DVD and do NOT provide the license key during the setup (otherwise you will get error for invalid key!!!)
d. After the installation is finished open HKLM\SOFTWARE\Microsoft\Wi
e. Open cmd with administrative privileges and type there slmgr rearm
f. Wait until restart is prompted (can take a while) and restart
g. After that go to System Information (windows + pause buttons) and under product key type your upgrade key and activate it
