For those of you wanting to take a backup of your desktop/laptop prior to upgrading to Windows7 there is a migration tool which you can run which will backup your documents and settings to a file (which can be located on a usb drive/network drive etc). There are many advantages to installing a fresh copy of Windows, I always find a fresh copy results in a healthier laptop.
The executable is migwiz.exe and there are two options to chose from which are fairly self explanatory, the first being where to backup the data (I suggest a network drive) and the second being what data to backup, I suggest everything. The migration wizard creates a single backup, so ensure you've got enough space for it.
After backing up your machine you can safely blank your machine and install a fresh copy of Windows 7.
Once you have a working Windows7 machine you can just double click the backup file and Windows7 will restore the data.
This is exactly the process I used to upgrade my laptop from Vista to Windows7 and it worked flawlessly.
Craig