There once was a "Buying a Used ZJ/G" sticky but it got lost a search should find it for you.
I had one for a few years and no major problems but age will mean you may have to do a bit of maintenance as to get it up to speed, regular servicing and low Kms is a good place to start, have a look under it to see if it has any bash marks. Give the thing a good tramp on the pedal to see if the auto changes smoothly and find a clear area to do some tight figure 8's to see if the CV's are making any noise. Look in the header tank, coolant should be clean with no tide marks from oil or other crap on the sides. Basically the same as for any 2nd hand vehicle. Check the codes by turning the key on/off 3 times , the odometer should display a number or done.
Also here
http://www.ausjeepoffroad.com/forum/...d.php?t=107891
Moorey has heaps of links.