I apologize in advance for offering a Windows-centric tip, but this one stumped me for long enough that I thought it worth passing along. Here's the setup:
I have a PC running Windows XP Home Edition and although I could make my Macs see the PC, the PC refused to recognize my Macs running Panther. After mucking with various network settings on the PC and Macs I decided to check the SMB sharing settings in the Directory Access utility (found inside the Utilities folder).
It's a lucky thing I did because when I selected SMB in the Services tab and clicked the Configure button, I discovered that the Workgroup entry in the resulting sheet read WORKGROUP (Windows' default workgroup name). Because my PC's workgroup is called MSHOME (the default name for a workgroup created with Windows XP Home Edition), the PC couldn't locate the Macs. Changing the Workgroup name in Directory Access to MSHOME made my Macs available to the PC.