I found a spreadsheet of automation protocols and features. I don't know how accurate it is, but there are a few high end systems that communicate with CAT5 cables.
http://spreadsheets.google.com/ccc?key=pq2S8fvu2JXEv1Ne9TIQhdA&hl=en
There is actually one down the street from me. It uses low voltage switches that all route back to a control room located in the attic (of this particular home). It was built in the '60s and is a very large custom home. But I have also seen the same type of setup used of a HGTV program as well so it apparently is still used.
I am not sure... but I think those systems are well suited for really large homes and NEW construction. A small gang of numerous pushbutton lowvoltage switches... is more pleasing to look at than having to mount a breaker box near a rooms entrance to handle a large volume of light/device switching (often done in commercial setups). Maybe that is what the OP is dealing with... and I misunderstood. But it would be less than common for someone that refers to themselves as "relatively young" and references "one room that's about 15x17".
Maybe it's just me. Maybe I've read too many posts that are really about Linux... and NOT Home Automation at all. Many seem to me to be anti-Microsoft, anti-corporate profit, anti-American.
I read here where someone performed some UN-described test in one 15x17 foot room.... and found X10 to be unreliable. And we here at the forum (that actually USE X10) know that is not true. So maybe that jades my belief in the remainder of the posts.
I just don't think a homemade DIY "relay and CAT5" setup.... sounds like something the building inspector would be thrilled with.