Granite Digital (
www.granitedigital.com) sell a "special" high quality 10m (about 32') firewire cable that RRPs for US$89. I'm working from memory here, but I remember reading in one of the Hard Drive manuals that over cable runs of 4.5m you need to use a lot of shielding to prevent data errors.
Granite also sell repeaters and hubs, which you could use to give you more cable length.
Hope this helps.
Cheers,
headwerk'n.