This is an excellent ride, some steep climbs and gravelly/rocky madness to get past, with quick swooping runs mixed inbetween. I'd advise taking a GPS and marking the car to work your way back, since this trail turns into a network up high on the mountain and runs into the Otero Canyon trail. Be prepared for weather changes and watch out for cougars and bears.
From Albuquerque, take I-40 East to the Tijeras exit, Go straight through the intersection and you'll be on Highway 337. You'll pass a ranger station on your left (if you're there M-F you can stop and buy maps of the area) and keep going. You'll see a sign on your right that says Tunnel Canyon and a parking area just past it. Should be approximately 2.63 miles from the first intersection off of I-40. Park here, trail starts by the sign.
http://www.singletracks.com/item.php?c=1&i=1901