Britespark.
we do a hell of olot of CCTV installation work and we personally only use RG59 on shortish runs, and all cameras are on 12VDC.
the power supply units are fully rectified and regulated DC and are positioned as close to the camera as possible, but some installs we place the PSU by the main equipment and feed the camera via two core 1mm flex (under 100m) with no trouble or loss of picture quality.
all cameras are usually 480TVL and are fitted with Direct Drive lenses.
as to using Cat % or even Cat 6 this is not a problem, all you have to do is use a BalUn (Ballanced to Unballanced) connection unit to each camera and back art the Multiplex and or DVR (Digital Video Recorder.
the company we use is COP, details can be viewed on
www.cop-eu.com htey are very helpfull and have an excellent technical department, (and they are cheap, but very good quality equipment because they make it them selves!!)
if you need any advice just ask.
Britspark