Use TCP/IP, matter of fact I don't think you have a choice. You'll need software on the Macs so they can share files with the PC's. Don't remember the exact name, but it's in the networking articles on this site. I'm pretty sure you can share print access the same way. If you're looking for the "cheap" implementation, then you only have two topologies to choose from. Star and bus. Any type of redundancy would be nice, however, is more expensive. What's going to get interesting is if you want to share internet access. Whichever computer functions at the gateway is going to be a very busy box.