If you have to do a clean install... which is recommended by the most experienced here as well as Microsoft, here is some info you may find useful. It's a partial quote from
Windows 7 Tweaks, Tricks, Tips, Secrets, Shortcuts, Solutions and Fixes
Install Win 7 from a bootable 4gb USB drive with 1 click.
* Download UNetbootin tool (free) from here:
Download UNetbootin, Universal Netboot Installer from SourceForge.net
If your upgrade is from Digital Rivers, you'll need to put the files in an ISO format first.
Run the tool, and browse to your Windows 7 ISO image file and click OK and
select the drive letter of your USB. That’s all!
It takes about 15 minutes to finish. (Remember the boot sequence in your bios
must be set to use the USB first.) Windows installs in about half the time
from USB... even the cheap ones read about 25 kb/s ...while dvd reads about 5
kb/s
3 days after Microsoft released Windows 7 they were getting so many tech support
calls about upgrading problems that they - basically copied the Unetbootin utility
*idea* and released one that does the same thing. However they were found to be in violation
of open source code standards and had to remove it from their website. However, it's
still available if you Google because once you let something out on the Internet.... well as they say
information wants to be free. Note: in releasing this utility Microsoft re-wrote their EULA in
regards to using an UPGRADE key with a clean install. They are working on re-writing
this utility from the ground up, using their own code. For those who don't know about
Unetbootin it is a very useful tool, especially for someone running XP or installing on
a laptop.