Rhode Island? Check out
http://www.riohva.org/
For woods racing/riding, check out
http://www.netra.org
There's bunch of links to dirty info from there.
If you've got a dirtbike, there's a race (hare scramble) this coming Sunday not too far away from you, in Union, CT.
http://www.netra.org/schedules/NutmegHS.pdf
If you're not into woods, there're a few MX practice tracks around. For big stuff, check out
http://www.ctmotocross.com