For $5, you can park in the Dowling parking garage, which is on Boston Avenue just north of College Avenue. (If $5 is too much, there are meters and even a few free spaces around Davis Square; you can park for two hours for $2. The T directions will tell you how to walk from Davis.) From Dowling, walk a half block southeast to College Avenue and turn left. Continue on College Avenue and cross the railway line. Halligan Hall is the large brick building on your left (it's a former radio factory).
The entrance for the CS department is at the southeast corner of the building; that's the corner closest to you.
If you don't like mazes, walk into the front door, go upstairs to the CS office which will be on your right as you leave the stairs, and ask someone to call me or take you to my office.
The entrance to Halligan Hall is near N 42°24.475' W 71°06.950'.
The garage at Dowling is at N 42°24.541' W 71°07.096'.
My office phone number is 617-627-4923.