This excerpt taken from the HPQ DEF 14A filed Jan 29, 2008.
From Points South via I-93:
Heading northbound on I-93 towards Boston, take Exit 20, which will be immediately after Exit 18. Follow the signs to "I-90 East." Take the first tunnel exit to "South Boston." At the first set of lights at the top of the ramp, proceed straight onto East Service Road. At the next set of lights, take a right onto Seaport Boulevard. The Seaport Boulevard entrance to the Seaport Garage will be ahead on the right.