What do you need to do to browse UNC shares on a windows 2003/2008 server from a windows mobile device?

I have verified network connectivity, can ping the server and I can browse shares of a Vista & XP Machines on the same network.

The server systems (2003 & 2008) dont seem to allow it. I have also seen posts about disabling "Microsoft network server: Digitally sign communications (always)" and this doesn't seem to help.

What is the trick?