Land Rover experiences are the best for anyone just wanting a taste of off roading. You can specify what you go round in, a 90/110 will be best to get a feel for it but a D4 is and awesome tool off road you just feel detached from it and the truck does all the work. Driving experience is no concern all they asked for when we went was our driving licence including the counterpart.

Rockingham is a great site and you have a nice drive round the grounds to get between sections. I've done it in a 110 and i'm due to go again in the new year to drive the new models.
Another option is slightly different and will make a weekend away worth while - http://www.kankku.co.uk/as/off_road_convoy.htm I know a guy that done this and enjoyed it but it doesn't offer the same "off road" experience.