I had to restore Vista on a Gateway PC.
Afterwards I was re-installing Microsoft Office Plus 2007 and encountered the same problem of "Proofing.en-us" not found. I would search for it and could locate on the installation CD. When I would cut/paste the folder path and submit I would receive "Invalid Path".
I checked the CD (It had a slight gash on the very edge).
I cleaned the CD.
Inserted it in a second CD drive on the same machine and start the install again.
Worked fine that time.
I plan on making a copy of the CD if possible.
I do not know if Microsoft will replace the CD (but I am going to ask).