Don't know if you're still looking for something to do this, but I wrote a Joomla! component and CB Plugin combo that will redirect users on login based on their member group.
You can find the package and documentation at
KeithsCode.com
.
As for creating additional user groups, you may want to look into JACL Plus for Joomla! to control User Groups and access levels for Joomla!
Let me know if you decide to use the Component!