I can completely relate with your problem and really wish that Microsoft Office checked on a per-application basis, rather than just one big check for all applications simultaneously. There is a relatively straightforward way to delete your reg key and get Microsoft Office to ask you to re-enter the serial number.

There's one tricky step, however, because you're going to have to open up your Terminal application and *gasp* type in a command or two.

Let's just jump in. I'm confident you can do it!

Open up your Applications folder, go into the Utilities folder and double-click on Terminal (or, possibly, Terminal.app depending on how you have the Finder configured). It'll look like this:

Now you'll want to move to the following directory:

/Applications/Microsoft Office 2004/

which can be most easily done by quoting the above, and using copy and paste. It'll look like this:

Now you're in the right place to get started.

--> Wait! Make sure you aren't running office at this point! <--

You good? Good. Now you need to go one directory deeper, into Office, and delete the file "OfficePID". At this point I'll switch to showing you what you type and what you'll see in response:

So far, so good. Now you need to back up a ways and delete three more files, but in a different directory.

You're in the right place, now just delete the following three files (again, use quotes to make sure it works right):

That's all you should have to do. Now just restart Microsoft Office and it'll ask you to reenter your serial number and you'll finally be free of this annoying problem!

Thanks to Creativetechs for this information...