You are probably looking at a Kramer matrix switch for VGA, they work with component video. You'll need a lot of baluns, sadly. I do not know of a cat5 hub to do this, but very happy to be corrected. You could try PM to 'Twisted pear' He is Mike from Madnat.
I'm sure that I've seen Gefen do a cat 5 send and receive HDMI device (at least they intend to...sure it was at ISE in February). I'd imagine you could pair such devices with with an HDMI or DVI distribution system.
Have a look at the 9870 or 9860 series from Audio Authority.
Demo'ed one a while ago, looked pretty good and will transmit HD component & audio up to 1000ft down 2 CAT5s'
Different versions can take digital audio or remote senders and have distribution amps built in.
Be warned the HDMI solution is EXPENSIVE. It works well, no question, and it's the only way if distance is a problem, and with whole house distribution of digital video it's almost bound to be. One of our installs has spend over £5000 on this alone recently, just for the hardware.
I find that most of my clients accept that an HDMI multi-room solution is going to be more expensive than composite video, so the price is not so much an issue. I just need to make sure that the HDMI solution I propose is of a suitably high quality.
Absolutely, I think the 5k here is a drop in the ocean. I mention the high cost because a lot of the forum users do have budget constraints, and getting them excited needlessly is not the best thing. That's a fair sized house we are talking about, bigger than most, but still, it's a pile of cash, and still doesn't include the wiring infrastructure, 3 cat 5's to each room (2 for HDMI, 1 for control) and a huge patch panel. The hub would not fit in my cupboard under the stairs.