On both machines, you'll want to go to the Appletalk control panel and make sure it's set to ethernet, and also see if you can make sure that the file server is actually enabled over IP, instead of appletalk-only.

Lastly, if you're doing all manual addressing, or if you're going to be using appletalk, having a router won't have anything to do with it. Although, a router is fun/necessary if you want the machines to use other TCP/IP applications such as web browsers, ftp/telnet clients, etc.

But, another vote here for the BEFSR/BEFSX41 from linksys. I've got a BEFSX41 and it's just fantastic. I've been using it for three years with minimal, if any hiccups.