Hi there, a few points.
1) If you haven't already run the cable, run CAT7, no one uses CAT5. You can get it for 40p a metre, and then you're future-proofed up to 10 gigs connectivity later on, if you leave enough slack to cut off connectors and re-terminate with future hardware.
2) You will waste a fortune on audio / video baluns for distribution over twisted cabling, and it will never be that great. (but CAT7 would give you teh greatest run lengths).
3) It's 2008 - we send digits on cables, not audio / video

Get a NAS (use any old clunker of a pc with a big hard drive). Get a half-decent one-gig switch and run your cables all back to a central location.
Hey presto - audio / video / text / pictures / pdfs / whatever you want available everywhere. [Use a cheap media streamer in each room like Showcentre 250 or the D-link / Netgear things]. Sonos is very good for high quality audio
hope this helps !