Should I build an Excel 2000/2003 version?

As I build Time-Creator, I'm wondering if I should make the software work on Excel 2000/2003. The first requirement is that you need a copy of the software and I have one on an old laptop.

The second is will there be enough customers that use this version to make it worthwhile?  I've started on making my program compatible but then realized it's taking away from my main focus.  I could always come back to it.

As I'm working on it I'm finding a number of compatibility issues with the VBA code I'm writing using Excel 2010.  The biggest ones are:

•  Ribbon isn't available in the previous versions
• Callbacks don't work 
• Sort command issues
• New bugs introduced by changing code to support Excel 2000

I've met my first goal to get out a version of Time-Creator that user's can download. My second goal is a bug free version and third is a version that's easier to use.  The Excel 2000/2003 version will have to wait unless I hear back from lots of users who want it.

Though, it's very tempting as I've spent around 5 hours already on this I may try to get out a version.

What version of Excel do you use? Should I build an Excel 2000 compatible version