Senior Paper Monitor,
as this will be rarely required it would be much more time efficient than loading all the documents to the intranet.
I assume you will therefore be intending to maintain backups of files located on client computers ?
Also, out of curiosity, why are you re-inventing the wheel when there are only 3 users involved ?
But I digress. Try a "file:" link. I think that's what you're after... e.g. file://UNC/PATH/HERE/ .... although I've got a niggling feeling what you're trying to do might have been disabled a few years back in IE due to security risks (not sure if it works if you add your site as a trusted site). You may therefore need to look at some form of signed Java applet, or similar in Silverlight or whatever.
Edit to add:
Ref. Silverlight, see "Sample 3: File Surfer" towards the bottom of
this website page which should give you at least a small insight as to what you can do with a signed Silverlight app.