How to use Upgrade Windows 7 to do a clean install.
1) select custom and do not enter key, Then
.. A) method 1. After installation re-run the Windows 7, but this time select Upgrad and ENTER you key this time.
.. B) Method two, preferred method for SSDs:
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How To: Use Your Windows 7 Upgrade Disk On a Fresh PC
How To: Use Your Windows 7 Upgrade Disk On a Fresh PC
Posted 10/27/2009 at 8:30am | by Justin Kerr
48CommentsPrint 105 118Share .Installing to a Fresh Drive
Step 1 - Access & Edit the Registry
A true geek has never been intimidated by the registry, but lets face it, it's a mess in there. To access the registry you will first need to open up the start menu and type "regedit" into the search field, followed by enter. To find the proverbial needle in this haystack, you will need to navigate through the tabs listed on the left in the following order:
HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Setup/OOBE/ . If you don't like doing it the hard way just click Edit then Find and type MediaBootInstall into the search field, and press enter.
Once found, double click MediaBootInstall and change the "1" to a "0". Once you have finished this, simply click Ok and close out the Registry Editor
Then
Before we try to activate our copy of Windows, we need to reset or "Re-Arm" the activation sequence. To do this, simply open up the start menu and type cmd but instead of just pressing enter, you need to press "Ctrl" + "Shift" + "Enter" to run it as an administrator. You can also accomplish this by clicking the start menu, typing cmd into the search box, then right clicking the command prompt application and selecting Run as administrator.
Once the command prompt appears type slmgr /rearm and press enter. Next simply type Exit and hit enter again, after which it will ask you to restart your machine.
Above quote is from MaxiumPC:
http://www.maximumpc.com/article/howtos/how_use_your_windows_7_upgrade_disk_fresh_pc?page=0,1