This page just details my own small home network - with a Linux, Mac and PC machine, all working in harmony and able to directly access each others drives and exchange files. Here's how I did it, and at the end, I'll suggest a few alternative ways.
So what I need is a way to link my three boxes, be able to exchange files freely between them (such as to back my Mac laptop onto my Windows PC), and provide a single access point onto the internet.
Firstly, each needs a NIC, and a hub. The Windows and Linux box both have 3Com NICs, and the Powerbook has one built in. I also bought a Bay Netgear 4 way hub. Either way, the machines all need IP addresses. I chose to go with a pretty standard static IP addressing system of 192.168.0.x. Yes, I could have gone DHCP, but for 3 boxes it hardly seemed worth it.
This is the main machine as such - fast and running Windows 2K with an ISDN TA into a flat rate ISP :-). This isn't running anything special really, just a few shared folders and a small proxy server to allow internet access to the other PCs. It's great for doing fast backups of the Powerbook stuff.
A couple of things need to be done here. For one I installed DAVE from Thursby Software, which gives the Mac a NetBIOS system which will enable it to access and be accessed by Windows PCs. Also, the TCP/IP needs to be changed, as do the proxy settings for many of the Internet apps.
This is much simpler - and cheaper - than the Mac solution, I simply fired up the Linux Samba server, and attached to the shared folders from the Windows box.
From here then I can simply share folders out across 3 systems for file sharing and via the proxy, all 3 can simultaneously connect to the internet 24hrs a day - very useful for SETI :-). What I tried to do though was have the Linux folders as the main swapping area, although backups of most of my files were written on the Windows 2000 PC, mainly because it had the CD-R burner, for making backups.
The benefits of this system are obvious: a relatively transparent way to share and backup files over 3 very different OSs. The downside - gets a bit fiddly, especially on the Mac, using DAVE which can be a bit weird sometimes, though to be fair to it's designers, this isn't quite what it was designed for.