That said, anything that allows me to extract cab files and get FS2004 working properly is probably well worth the effort.
Try the evaluation version of WinZip.
http://www.winzip.com/downwzeval.htm I notice it now has a time limit but 21 days should be long enough to open those CAB files & see if that fixes your problem. Of course, there is no guarantee that it will.
It occurs to me that a full Uninstall/Install of FS9 would have been a lot quicker than all this messing around.

PS. Many people seem to like WinRar for some reason.
http://download.com.com/3000-2250-10007677.htmlI tried it once but don't remember if it will open CAB files. I prefer WinZip myself & wouldn't be without my fully registered version.
PPS. As CAB is a M$ format I'm surprised that the WinXP unzip utility cannot open them.