I'm not sure what codec was used to make the carshow files. My media player looks for a Codec as well, gives me an error, but then plays it anyways. I've got Windows XP at home, and DIVX installed. But, at work, I have a brand new machine, with just Windows XP, and service pack 1 on it, and it still works even though I get that codec error as well. I haven't installed any codec's on my work machine. Well, besides quicktime 6 but that's got nothing to do with it I don't think.
I tried on a Win98 machine last night at the Dealership ( the guys wanted to see it), but it never worked in windows98. I never had time to play with it.