In particular should I run power cable to them - or power them over cat5?

Thx 

There's loads around,

http://cgi.ebay.co.uk/New-Camera-CCTV-2-Video-Balun-Transmit-Receiver-UTP_W0QQitemZ200172149563QQihZ010QQcategoryZ60839QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

ebay has loads of rj45 baluns's it seems pretty common to run the power along side.

There's even a 4 box solution for 4 cat5e with power in one box.
 

This is just an example of aan external, IP camera with poe CAPABILITY.

Look down page at second camera. 

http://www.ipcctvcameras.co.uk/POECameras.htm

Then only single cat 5 cable required. You will need a POE injector or a network switch with POE capability.

cost circa £200, there may be cheaper but with a device in an external case ready to go i suspect not much cheaper. 

 8 PORT SWITCHY WITH 4 poe PORTS http://www.ebuyer.com/product/132965

16 port http://www.ebuyer.com/product/83818

please check specs on later as not obvious whether all ports poe or just some.

One quick note of caution on 'consumer' IP cameras - they tend to have very poor low light performance - whether that's an issue depends on your intended use of course!

 I have an Axis Mega resolution camera turning up tomorrow. 1280x1024; I've had monitors with less pixels!

Are you happy with it?

What spec / price?

Intereasted to share your thoughts

Thx