It's been a while since I had Office 2003 installed... However, there are two routes to uninstalling/disabling add-ins. I'd try them in this order:
1. Disable the add-in from within the parent program (like Acrobat). You'll need to make sure that NO Office programs are running, including Outlook. You MAY have to re-run the parent program's installer and either customize the installation or repair the installation. This is how I used to have to deal with Scansoft/Nuance's PDF Converter Pro plug-ins, for example.
2. If the above doesn't work, if I recall correctly, you need to go into each Office 2003 program and click on Tools and then look for an "add-ins" entry in the menu. You might have to go to Advanced Options (can't remember - I do remember that each program is slightly different, or at least Outlook is different) and then look for add-in entries. The add-ins themselves are COM add-ins and/or something like EXCEL add-in, POWERPOINT add-in, etc. They changed all this radically with Office 2007 and I've been using 2007/2010 for almost three years...
A third option, if you know the name of the add-in, is to search for them in the Office program directory. They're usually stored in folders, something like: "C:\Program Files\Microsoft Office\Office11\ADDINS\" but there are other places as well, for example: "C:\Program Files\Microsoft Office\Office11\STARTUP" and "C:\Program Files\Microsoft Office\Office11\XLSTART". Finally, some add-ins get installed into their own Program Files folders, so keep an eye out there, too. E.g. Acrobat add-in files *might* be in a folder nested in the Adobe folder (C:\Program Files\Adobe\Acrobt...).
*I'd be VERY careful going the third option route above because you can wind up with references to deleted add-ins that remain in the Office application*
Hope this helps...