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#181
Under the EULA you have to stop using the Vista when you install Win7. That said, there is no way they can enforce it. But a lot of guys are coming here wanting to bail out of dual boots within a day or two after trying Win7, and it is a messy job which involves having to delete Vista off the first partition then move Win7 over onto the first one.
You would get a much cleaner and more permanent install by backing up your files and gathering your program installers, booting from your Win7 Installer, choosing Custom>Advanced tools and delete all partitions, create one big new one, then format and Install. The WIn7 disk will have already scanned your HDD to see you had Vista and pass a flag to accept your key and activate. This is the cleanest possible install.
After the job is finished, whether you dual boot or clean install, use Win7's new Backup Imaging utility to save an image of your HDD externally so you will never have to reinstall again (unless you choose dual boot and later Vista removal messes up, which it might).