FMP 5.5 Windows Client Can't Connect to FMP 5.5 Mac Server

[btlyles]

The Setup:

- FMP 5.5 Server running on Mac OS 9

- Router set to pass port 5300 to machine running FMP server

The Problem:

Can connect to the server from Win and Mac clients on machines on our LAN. Can connect to server from Mac clients outside the LAN (via IP address). Cannot connect to server from Windows clients outside the LAN. I enter the IP, get the little "trying to connect" squiggly, then nothing. IP address is added to server list, but no databases show in database list.

Suggestions? Thanks!