I know this is an old posting, but thought I would respond anyway.
There are some good trails at the end of Oregon Trail in Garner (27529). (Just a few miles outside of Raleigh) You can park at the end of Oregon Trail, because it's a public maintained road. The ill-tempered lady at the end of the road might tell you it's a private road, but according to the Wake County Sheriff's office it's public. Me and my friends have been going down there for 15 years and never had any issues. You can legally park all down the left side of the road, but might want to stay out of the yard to the right. The trails go for tens of miles, and lots of challenges for an ATV or motocross.