Just a quick note:
Pierre - if you have a PC, there are plenty of Firewire
addon cards for a PCI bus. Check www.newegg.com and type in "PCI firewire card" in the search box. You can pick one up for about $20. I'd hate to see you limit your choice of scanners.
One difference by the way between the Epson 3170 and the 3200/3200 pro is that the 3170 is NOT supported by Ed Hamrick's fabulous Vuescan scanning driver, whereas the 3200 is. (Ed says they used a weird command set and won't give out any details, so I'm not sure it will ever be supported.) Check www.hamrick.com for information about Vuescan - people over on Usenet in comp.periphs.scanners swear by it, and I do too.