The Baltimore Chamber Or chestra will join in the world wide chorus of "Happy Birth day, Dear Wolfgang" - Mozart was born 250 years ago - with a performance of his Symphony No. 41. BCO music director Markand Thakar conducts the program, which includes the Pi ano Concerto No. 1 by Shosta kovich with Moscow-born Boris Slutsky as soloist. There's also room for a string orchestra piece by contemporary com poser Aaron Jay Kernis. The concert is at 7:30 tonight at Goucher College, 1021 Dula ney Valley Road, Towson. Tick ets are $28. Call 410-426-0157.