Originally Posted by ajhieb
Cat5/6 will work.
Personally, I don't think CAT5 is acceptable. Too slow, and with so many network tuners independently sending HD streams TO the router, and then FROM the router TO the HTPC, not to mention the other slew of HD streams from the HTPC TO the router and then FROM the router TO extenders/HDTVs around your house... well you get my point.
Honestly, if you want a reliable glitch-free problem-free setup and you're going to have at least six network-based tuners for recordings, while you're going to be independently watching previously made recordings on 2-5 HDTVs around your house... you've got to build a CAT6 gigabit-router network.
Ethernet-over-powerline approaches are commonly limited to 100Mbps, as are ethernet-over-coax. These are the usual substitutes for true ethernet cable home networks where you can't or haven't run ethernet cable through walls or ceilings, and perhaps have an old RF 75ohm coax from the old cable days that gets to the target room and has another end near your router. Ethernet-over-coax is also limited to 100Mbps streams, though there may be multiple of them.
And of course powerlines run through walls throughout your house, but probably also go through circuit breaker boxes (unless you're lucky and find a direct-copper link from one room to another in the same part of the house) and may or may not be grounded properly, etc. So these may or may not work well, depending on distance from a power socket near the router to the target room. But you're still talking 100Mbps, which again is impractical to support a 6-tuner network box from any vendor for an HTPC setup.
Word to the wise: home CAT6 wiring is something you should most seriously consider if you want to build out your own whole-home HTPC-based setup. You can get by with CAT5/CAT5e to the extender/HDTV nodes, but from HTPC to/from router and network-based tuners to/from router, in my opinion you want CAT6.