Members of one workgroup should not be able access shares in another workgroup. Can they? Of course, there is no way, short of watching them, to stop a user from changing the workgroup on his or her computer. If you want tighter security your practical choices are:
1)Physically separate the network.
2)Change from share-level to User-level access (Start, Settings, Control Panel, Network, Access Control)
3)Purchase a file server and set-up a domain, etc.
4)Develop administrative procedures and trust your users to abide by them
The second two depend on passwords. Larry