See this kb article:
You receive a "Installation Error: File not Found" error message when you try to convert the Office 2003 trial program to the full product version of Office 2003
Note The Pa561401.cab
file is the file that is most frequently referenced in the filename.cab placeholder of this error message. http://support.microsoft.com/kb/896301
When reading the info on link (and sublink found within) provided, please pay special attention to why the moscache folder is used in the first place and why it may not exist now.
If mos cache is there and this cab is the only install hangup, I did find this: http://www.harrythompson.com/ZF561407.CAB.htm
If this was a trial version
and the time has expired
, and you have thought that if you uninstalled and reinstalled this you may recover the use of the program, your dead in the water. A secret spot in the registry always knows when this is being attempted.
Noted some problems if trying to update office but once again it will look for the source of the original install. This maybe moscache or original cd's. http://www.google.com/search?num=100...AB&btnG=Search