You can do this easily if you're using Active Directory. The feature you're
after is called "folder redirection" and it's in Group Policy.
If you're not using AD, you can do it on an individual user basis by editing
the following key in the registry
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User
Shell Folders
The value you're after is called "Desktop". A location of the form
\\server\users\%username%\desktop is probably what you need. Otherwise,
using a drive mapping is fine as long as you're certain that the drive will
be available when the user logs in.
As always, back up your registry and machine before changing it.
Regards
Oli