Linux on both ends, plus MythTV.
SuSE 10.1 includes a working set of backend plus frontend. I'm using it here - twin analog TV cards and a big dedicated IDE HDD in a 64-bit Sempron machine as the backend/server machine (which also has a 2nd big screen in case I want to run a frontend in this room - in fact that's where I'm sat right now, watching the evening news on the left screen while I type this). The sole dedicated frontend is in the bedroom - a lowly Duron-1200 with chipset-integrated SiS graphics and a PCI WLAN card.
You'll need about 2.5 MB/s stable throughput on your WLAN, else you better forget that idea.