Had the same problem...fought with it for a few days...I have set up small networks before so I knew about the workgroup thing and some of the sign on issues when challenged by other computers on the network...etc...etc...was just about to try removing and reinstalling Client for Microsoft Networks when I decided to do some "Fishing" online and stumbled into here...I say all that to say this...
FORKING THANK YOU New Guy_1
This WORKED LIKE A CHARM!!!