Welcome Bugglet.
Firstly find one to teat drive, so if its a 2003 your looking for, test drive a 2003 - 2005. You'll then get a good idea about the power and interior.
Ask the stealer to let you have it for a good few hours and try it on the motorway, in town and on the back roads.
Plus make sure the one you test drive first is not the one you buy and give it a damn good ragging, so you really get the feel for it.
If you buy one from a trader, make sure you get warrenty and make sure they will ensure the axles, syncros and stereo is covered.
Look out for the poor paint work on the bumper
Take a CD, I use Fatboy Slim, right here right now, whack it in the stereo and crank it right up and listen to see if any of the channels or sub has gone
Try the aircon, heated seats, check for tools, jack etc
Again as before, someone else will come along with more advice
Cheers and good luck