The Advanced Computing for Science Department is in Bldg. 50A & 50B on the second and third floors. Building 50 is composed of ~6 connected components identified by letters. Bldig. 50B is the southern-most and 50A is the northern-most of the two green, six story buildings that are the first building on the right after entering Blackberry Canyon Gate on Hearst Avenue. If you are coming by shuttle bus, it is the building directly across the street and slightly up hill from the LBNL stop.
Deb Agarwal's office (2276) is at the south end of the second floor. The division office is on the 4th floor of 50B to the west of the elevator. The department admin, Gail Maeda, can be found in 50B room 2231. They can help you if you get lost.