will I be able to use my upgrade serial number

I have preordered a copy of W7 Home Premium and expect to recieve on 10/22. I have installed a copy of W7 Home Premium RTM in a clean install after removing Vista Ultimate. Will I be able to upgrade the RTM copy on my computer by just entering the serial number and then activate it or will I have to do another clean install and use my Vista disk to prove upgrade?

I don't know.

If it's the same as Vista, you will *not* be able to install the OS, and enter an upgrade key later.

I believe that you could enter the key for a full license, but it appears that you ordered the upgrade license.