Motocross shouldn't be anything new to locals. During the spring and summer, you can find dirtbikin' kiddies to well-seasoned mudders hopping around dirt mound tracks all over the quad-county area. But hold on, this is where "Best Bets" takes on the echoing deep-voiced edge of a monster-truck announcer: You've never seen motorcross biking like this before! Ultracross is coming to the Raleigh Entertainment and Sports Arena! Catch the eardrum-popping thrill-a-minute excitement of extreme motorcross racing, this Friday-Friday-Friday and Saturday-Saturday-Saturday, March 17 and 18. See riders hurl themselves around the track at breakneck speed, with NO HOLDS BARRED (use your imagination)! Don't turn your back on alternative sports. The guaranteed adrenaline rush will do your heart good. Call Ticketmaster, 834-4000, for information.