Mapped Drive double click results in Autoplay instead of Open???

I have a small home office network with an XP Pro SP2 PC sharing file folders
to the network. All other computers are XP Pro SP2 of varying types. There
are 4 folders shared out to 5 other PCs. System 1 can double click on Public
folder and it will open, but not the other folders... it will receive "Open
With" dialog box. I have checked for autorun.inf files and there are none.
It gets more interesting as I move to PC2, where double clicking on public
will result in "Open with", but a different folder will be able to open
correctly. Now on PC3 no mapped drives open correctly. PC4 has public and
another drive that work correctly. PC5 opens a different folder than the
others, but only one correctly. If I right click on a mapped drive I get
menu option with default of OPEN for the drives that work properly. On the
drives that give me "Open with" the menu default is AUTOPLAY. None of these
drives are optical drives as a source, and are all contained on one physical
drive. I cannot find anything about the registry entry to change this.

Please help,

Jason

Have you checked the NoDriveTypeAutoRun registry value?

91 = default
FF = Nothing autoruns (and my advice!)

Exists under computer, and under each user.

Problem is not effected by AutoRun registry value. Was already set to "FF".
Any other ideas?