I take it you are talking about insert rather than import?
Try something for me just out of curiousity....
Open Windows Explorer and navigate to the c:/ and open so you can see the contents of the c:/
Now click the View menu,
What is it set at large icons, small icons, list, details or Thumbnails?
If it isn't already change the view to Thumbnails and reboot the PC. (May not be required but hey lets be professional)
Now try accessing the insert in Office again.
What's happened now?
Check the settings you just changed against other systems are they the same?
If this doesn't work then service pack the PC with all the latest Office updates.
Still no joy then i would re-install Office on this users PC. (Could be he had a different setting during install although if you have 800 pc's i imagine you are using some sort of Imaging Software).
Last option service pack the PC.
HTH