I just ran into this sort of problem and finally got it resolved.
I found 2 different issues related to these type of problems. The resolution of your specific issue might be either one of these.
1. I was periodically erasing the Recent folder under ...\Documents and Settings\<user>\Application Data\Microsoft so that I didn't have to look at all of the last entered files and, as a result, I was somehow corrupting something that Word needed. The consequence was that the first time I went into Word after clearing out this directory and then attempted to Open a file, I would get an error message saying that this feature was no longer available and do I want to restore it from the Installation disks. When I quit clearing out the directory the problem went away.
2. This other problem occured at unusual times such as going into Windows 2000 Search or other programs that I had. It took a massive un-install of Office, a COMPLETE manual purge of the Windows registry of everything related to Office not removed by the un-install using Regedit, a Re-install of Win 2K, updating Win 2K service pack 2, running Regclean and Norton Utilities to "clean house" and finally re-installing Office 2000. Was all of that necessary? Who knows? No one on any other forum had any more specific suggestions and/or answers and it worked.
Good Luck,
jrbbldr