Hi.

I use both firewire adapters and external enclosure from EXSYS. I know these are available in the US as well, but I can't find a good URL for that. Anyway, the archos devices use the same FireWire-to-IDE adapter chip, so they should work just as well. And AFAIK, pretty much every supplier of such enclosures are using the same chips. So not much difference there.
The PCMCIA and PCI adapters are a different story though, but appart from that fact, I can't give much detail. I just know that some are making trouble, with DV camcorders especially. These FireWire adapters are available (without video editing software) as cheap (or expensive) as 50$ approximately.
I don't know of any standalone-fileservers for Ethernet that are even remotely near the price regions of USB/FireWire enclosures. Actually, you can get whole PCs for the price of those.

cu,
sven