GAINESVILLE, FLAfter 10 months of bitter, around-the-clock struggle, pizza-delivery driver and aspiring guitarist Darren Lowell, 23, has finally mastered The Rolling Stones' "Jumpin' Jack Flash," his upstairs neighbor reported Tuesday. "I'm glad he finally nailed it," neighbor Jeremy Quinlan said. "From what I could hear through my living-room floor these past 10 months, he was really locked in an epic battle with that elusive 'dunh-dunh, da-da-da da-da-da da-da-da' riff. It was truly like Ahab and the whale." Next week, Lowell is slated to embark on his next ambitious project, Van Halen's "Eruption," which is scheduled for completion in the spring of 2004.