Doesn't sound like a DirectX problem, but perhaps, there is shit that goes on in XP that I just don't understand.
I'd say try uninstalling all the codecs on the machine in question, and then reinstall just the ones that you know you'll need and see if the problem persists. Of course, even if it doesn't, that doesn't mean that it was the codec that was the problem, because who really knows what happens to other parts of XP when you uninstall/install software.
I swear, the more user friendly they make these damn things the more I struggle with them.
For Micro$oft's explaination, check here:
http://support.microsoft.com/default.aspx?kbid=234019