using any mods?
Try delete or move all files in Data\Movies\Intro...
Now you mention codecs... wasn't it once a problem for someone with a Kodec-Lite or something?
Worth a try to remove all added codecs...
It just doesn't make sense that an upgrade would do that to SHIII/IV. Normally a piece of cake to run this old software...
A last shot: do you have any yellow exclamationmarks or red crosses in your system properties?
I.e. anything with missing driver or not working?