haliparotin
Well there can be problems with Windows PC's when you change the network setting from a Workgroup to a DOMAIN. AFAIK you should start with a workgroup name that is different to the desired DOMAIN name. That's why I suggested what I did. (This is on the workstations).
Also after setting your DOMAIN name in SME server, you should also restart the server and restart all workstations.
Also have you enabled SME to be a PDC (DOMAIN controller for you whole network) ?