[Edit]Oh dear, i read Apache, not Samba. 😀 Well in Samba, I have nooo idea, not even sure it's possible. Especially since you don't really "download" through Samba.
** Old crap**
You could du it by using a small tracker and link to that instead of the file.
Like file.zip becomes dltracker.php?file=file.zip
The dltracker.php just increments the counter (in a file or database or whatever, your choice) and redirects to file.zip. This would however not work with direct links.
Another choice would be to parse through the Apache access logs to find the number of hits. This could get a bit messy though. 😉