I would suggest moving from Vista 64 to 7 64. Doubt there's much difference overall. and you'll be able to use 64 bit programs still. As far as I know, you should be able to seamlessly upgrade from Vista to 7. They had a chart on the net somewhere, and I think I originally saw it on Engadget.

Not the exact link, but it does your question justice: http://www.engadget.com/2009/08/11/h...tell-about-it/

Scroll halfway down to see the Vista to 7 64 bit upgrade. However, from personal experience, it's normally easier to just backup all your important stuff to an external drive, and then do a fresh install than upgrade. Who know what problems may arise if a file isn't updated properly.