Workgroup connection management seems flaky and erratic in Panther. Someone suggested connecting explicitly to a shared drive and this has worked well for me.
From one of the Finder pulldown menus (sorry, don't have a Mac in front of me) choose "Connect to a Server" and specify the servername and username as follows:
smb://user@server
If you know the name of the shared drive you can append that as well:
smb://user@server/sharename
If you omit the sharename, Panther will display a drop-down list showing all the shared drives available on the specified server. You can simply pick one from there.
If the Windows account has a password, you'll be prompted for it.
If the connection succeeds, the shared drive will appear as a new disk icon.