http://maps.google.c...ac04c5&t=h&z=12
Hi Rushadventures
I've been to Thetford Forest a few times, there is a place called High Lodge which is a sort of outdoor activities centre.
This is where you'll find the marked routes that skudupnorth mentioned.
It's located along the B1107 Brandon Rd, you do have to pay for the car park, about £9 all day per car. It is really good for single track riding, and there are a few "bomb holes" if you fancy a bit of the daredevil stuff
If you don't want to pay for a car park, then take a look at the link above. This is a route I recorded with MyTracks, on my Android phone when I did a charity ride.
If you look where it crosses the B1107 & B1106 there is some parking on the side of the road. Then you can just ride into the forest using the fire roads. Using a combination of Google StreetView and Satellite views you may be able to see more clearly.
This is of course for MTB's, there are loads of quiet country lanes around this area too for road bikes, but I'm not too familiar with that side.
Hope you get on OK, and tell us how you do.