Hi there Craig,
Sounds like something fishy is going on...

I suspect that you might be running afoul of a few errors at the same time, which makes the whole situation a little more complex. When you say "Older Computer" i start thinking along the lines of "what else might be stopping up the works".
Righto - to test this out, perhaps you can try installing and playing a DVD with a different media player. Windows Media 11 is a pretty resource heavy player, and is a bit particular about it's codecs etc... I would suggest that we eliminate the software angle by trying a different play - if it works then we can look into the Windows Media Player fault, if it doesnt then we can keep pursuing the hardware/driver angle.
Perhaps you can download an install the FREE media player VLC from
http://www.videolan.org/vlc/download-windows.htmlLet us know how you go!
Cheers,
:)RG