Avid Pro Audio Community - Windows Upgrade questions.

So I want to upgrade my system from Windows Vista 32bit to Windows 7 64bit so I can run Pro Tools 9. I know that you can just buy a Vista to 7 downloadable upgrade from Microsoft, but that you can't upgrade right from 32bit to 64bit. I've read that you can download the .exe file and burn it to a DVD and then do a clean install the way you would with any new OS. My question is: can you still just pay for the Windows 7 64bit upgrade and do that? I'm concerned that by doing the burn to DVD clean install method it wouldn't work because the downloaded .exe file is an upgrade and doing a clean install isn't upgrading the current operating system, but more so just overriding it. Would I have to purchase a full version of Windows 7 or would the upgrade version work?

Also, I ran the "Windows Upgrade Advisor" which told me my computer can upgrade to Windows 7 32bit. Im pretty sure that my computer (HP Elite d5000) can run Windows 7 64bit, being as it did have Vista 64bit on it before I realize that pro tools only worked on 32 bit. I'm assuming the Upgrade Advisor told me that it could only be upgraded to 32bit because I'm currently running 32bit Vista, but could it mean my PC wont be compatible with Windows 7 64 bit? Thanks for any help.