Can I install Windows 7 over Windows 7?

Hi, I already have the build 7000 up and running on my rig but I plan on installing the public beta version anyway, you know, just to make sure everything is in order.

What will happen if I run the Win 7 installer(this time, the public beta version, it makes no difference whether they are indeed the same version as to what I ran a week ago) and attempt to install win 7 onto the hard drive that already has win 7 installed?

I was able to select "upgrade" in Windows setup when I went from 6801 to 6956 and from 6956 to 7000. I think you'll get the option "upgrade" if there's at least one difference in the official Public Beta build. Btw, the upgrade went fine in all cases.
So , the answer to your question is yes.

Cheers

The answer is NO, you won't because it is the same build you already have :)