Get a router with ethernet and Home PNA( which runs off a your regular phoneline; make sure your phone cables have 4 wires on them). A
Panasonic router off CompUSA is $99 (1 port ethernet only), a Linksys is about $150. Add the cost of a HPNA PCI card ($30) or check
this out at Surplus computers for only $10. Windows Xp even has drivers built-in for them.
I currently have 4 PC's at home, two of them are hooked up thru ethernet and the other two (one at the living room and one over at the guest room). I use a Netgear RP114 router and a PE102 ethernet to HPNA bridge. This route is more expensive but since I really liked Netgear, I went with it

. My cards are the ones from surplus Computers.
Operation is transparent, the two HPNA PC's are like hooked up to 10mbs ethernet] while the other two are hooked up to 100mbs ethernet. 10mbs is perfectly OK for casual files transfers,
printer sharing, Network gaming and sharing my cable internet.