The file is not corrupt, quicktime alt. only works for winNT/xp/2003. There must be another solution. I'll see if I can find anything.
edit: It looks like Klite codec pack is compatible w/ win 98 that is what i would try first.
here is the download page
Free-Codecs.com : Download K-Lite Codec Pack 3.10 FULL, K-Lite Codec Pack 3.10 STANDARD, K-Lite Codec Pack 3.10 BASIC : K-Lite Codec Pack is a collection of codecs and related tools
But if that does not work there is always VLC player which doesn't even have to install on the sytem, I carry it w/ me on my portable hard drive and it works very well.
VLC media player for Windows
I hope one of the two get you going.