If I understand this correctly you have installed the Office Beta onto a machine currently running Office 2003 without first removing 2003 right?
What would have happened is that the Beta Version would have at the very least overwritten some important files even if you installed it to a different directory if you didn't do this it would have completely overwritten Office 2003.
If that's the case you'll have remaining Registry Entries on that computer that are very time consuming to get back if at all. When you try to remove the Beta Copy you'll most likely get some form of Error Message and the same will apply to the 2003 version of Office.
If that's the case here I wouldn't even recommend a Repair Install as the Registry will remain as it is and you'll be stuck where you currently are the only real answer is a [b]Wipe & Reinstall![/b]
You should [b]Never Install Any Beta Product[/b] on a production computer as you always run the risk of having to wipe and reinstall all the software. About the only good thing here is that you'll be able to save your existing data without a problem and don't forget your Favourites, Email & Address Book as well as any other Data Files that are locked up in different Applications like Accounting Software and the like.
Col