Sounds like a permissions issue. Do you get this message when trying to access a folder? What accounts do you have setup now, and what are their permissions?(both computers) Can you browse to other computer? I think we need more information on your setup details, and what exactly you are trying to do.
Anyways, here's a how-to guide on setting up a workgroup.
http://www.howtonetworking.com/workgroupsetup.htmEDIT: Also, Bleeping Computer has several other guides that may be helpful. Please look through the following section of our Mini guides and how-tos -
http://www.bleepingcomputer.com/forums/forum97.html