FireWire TCP/IP

I have a G3iBook hooked to a WindowsXP via firewire. I have Synergy running to share keyboard and mouse. I use the Apple for school and personal email while doing 3D CAD on the PC. I seem to lose my internet connection intermittently on the iBook even though I have a network bridge setup on the PC. I can reset the DHCP IP address and get the connection back but it will go out again. Any way to reset IP address via Unix command? Or is there a better way to connect the two together.

PS- Ethernet and a router are not options.