There are some really easy trails in Chatsworth area, Lebanon and Wharton State Forests near Rt. 70 & 72 (think they renamed Lebanon after someone, but I forget who). Lebanon is right across from the NJORVP off road park, Wharton is a little way down the road..
Its sandy, and there are a lot of dead end trails, so be prepared to back up.
It's a nice place to use 4wd without romping the crap out of your new truck!
There was also a place right in Jackson behind Great Adventure. We went back there on dirt bikes years ago. Turns out it wasn't legal place to ride, and it was patrolled. The Jackson PD had a Dodge 4x4, and when they came in to bust us, they got it high-centered on a whoop. We debated helping them get it out, then getting screwed for our efforts, but we did the right thing and helped them get it unstuck. The cops told us to enjoy riding there the rest of the day, but not to come back.
They also told us toxic waste was dumped on the site.
