On that I am not sure, I personally did a clean install as I prefer those, I am running it on a separate HD so I can boot between Visa and W-7, I would recommend a clean install format the disc and or partition you are going to install it on. Clean installs give you less chance of file corruption than an upgrade does. When W-7 comes out in October you will have to a clean install anyway or could upgrade your Vista. You will not be able to upgrade W7 RC-1