You've got three options:
Option 1 is a Ethernet to USB/Firewire adapter:
http://www.newegg.com/Product/Produc...82E16899888405
Option 2 is a PCMCIA card (if your computer still has one...) that gives you 2 USB, 1 Firewire 6-pin and 1 Firewire 4-pin adapter:
http://www.newegg.com/Product/Produc...82E16815124013
or this PCMCIA that just has 2 Firewire 6-pin:
http://www.newegg.com/Product/Produc...82E16815158010
another 2 6-pin Firewire option:
http://www.newegg.com/Product/Produc...82E16815150014
If none of these options are all that appealing, this is the search that I used through Newegg, there should be more available in those pages:
http://www.newegg.com/Product/Produc...page=1&bop=And
Option 3 is a hub with 4 USB and 3 Firewire ports that are routed through a USB port:
http://www.newegg.com/Product/Produc...82E16817111714