All newer versions of Outlook support the older 97-2002 file format. Just keep in mind that there is a hard size limit of 2GB for the old format. When you copied the file to the desktop did you also clear the Read-Only bit? (gets set when you put something on CD/DVD) You can't open a .pst unless the file can be written to.
Once you manage to get the file open I strongly suggest that you create a new format .pst and drag/drop the contents of the old one into it.