First off, I need to point something out. If all of you remember, I was not able to get my Vista to accept my GPO preferences. That is because I needed to install a new set of client-side extensions (CSEs). Once I tried out this problem on my Windows 7 VMs, no problem. You can get the Vista and XP CSEs here:
Windows Vista (x86): http://go.microsoft.com/fwlink/?LinkId=11185
Windows Vista (x64):http://go.microsoft.com/fwlink/?LinkID=111857
Windows XP (x86): http://go.microsoft.com/fwlink/?LinkId=111851
Windows XP (x64): http://go.microsoft.com/fwlink/?LinkId=111862
You will also need to install XMLLite on your XP SP2 or later machines.
OK, now on to the question. The answer is yes you can. I did find a condition did exist though. The folder with the users name must already exist in share on the network drive you are mapping to. Having to make all those extra folders manually totally goes against my business 2.0 attitude. You could write a script, but that would take effort. In the User preferences of that same GPO, is the Folder option. Using this option I created a new folder at location \\ServerName\ShareName\%UserName%. This time the mapped drive worked.