Can I install a 64 bit Windows 7 on a computer that currently has a 32 bit version of Vista? I think that my hardware can handle a 64 bit Operating System. I tried to install a 64 bit version of Windows 7 but the installation program checked my current Operating System and stopped.

Is there any way to override this?

How can I make sure my hardware can handle the 64 bit OS? (I build this computer from scratch)

I do not think this will delete my hard drive. Will it?

There is no upgrade path from 32bit windows vista to 64bit windows 7.
The only way is to do a clean install of the 64bit by booting from the win7 install dvd and selecting a custom install. This method will require you to backup all your data and re-install your programs.
You can find more info here: http://www.winsupersite.com/win7/clean_install_upgrade_media.asp

Ok to find out if your motherboard will handle a 64bit OS, do this, go to this site and download cpuz it's a free utility that will tell all your motherboard specs and your computer for that matter. http://www.cpuid.com/cpuz.php
also go to Device Doctor site that way you will get all your correct 64 bit drivers. http://www.devicedoctor.com/

Also do what laser said, almost forgot. clean install only for it to work.