Just use google earth. If it looks good from there, then most likely it is good. This is what I do:
1) Play around on google earth for a bit and find some tracks that look good.
2) Scope it out by driving there in the car first.
3) If (2) works out good, then time to ride there.
I've been to about three different spots now, and never came across anyone, except the last time I went, I came across some bush walkers, but you just wave your hand and don't ride like a dhead past them then it's ok.
On saturday I'm going to another place. It's a $2200 fine if you are caught riding there (plus probably the unrego/unlicensed crap), but damn it looks like a great place to ride! All the places I've ridden at so far are fairly rocky, but this new place I'm going to is nice and green without too many rocks. Ahh well, you gotta have fun!
Anyway if I get fined then I will post about it. I hear that they have choppers these days to catch people. What a bastard. Why can't we all just get along...