Hi Dean, If you have registered the office application, then boot to the old OS, login to this - [URL] with your Microsoft account details and uninstall the existing software and then install the application on the new OS. When you purchased the system from Dell, you would have received an MPI - Microsoft Product Identifier card along with the machine that looks like this - [URL]  Please check if the box that you received the system with, if you have not discarded the box by chance. If you are unable to find the card, then boot into the old windows where Office is currently installed, then download this program - [URL] - run the application, it should list the product key for office. Please make a clear note of the product key. Then uninstall the existing office software from control panel -> programs and features. Make sure you download the office installer package before you uninstall the existing software. Download office online or download a trial version and use this key to install office on the new OS. Either way, if the Office has been purchased with a single license, then you cannot have office installed on both the old and new OS. It can be installed only on one machine and on one specific OS. Let us know if you have any other questions.
I have a Dell XPS8100, which came with Win7 Home Premium (x64) and Microsoft Office 2007 (I think Student & Home) pre-installed.  Recently I upgraded to Win7 Pro.  I created a new partition for the new install, as that helps get rid of of old crud, but I still can boot the original partition w/ Offfice 2007. I would like to install Office 2007 on the new partition with Win7 Pro.  There is a 25-character key on the sticker on top of the computer, but when I try to use that on the Microsoft download page for Office 2007, it is rejected as eligible for download.  So, I don't know if that's the correct key or not. At any rate, I would like to know if Dell can provide a solution to this, without buying a new copy of Office.  The Dell-provided reinstallation discs do not include MS Office. 
Reinstall Office 2007