From the South: Northampton is on Route I-91 in Massachusetts. Take Exit 18, and follow Route 5 north into the center of town. Turn left onto Route 9. Go straight through four traffic lights, turning left into Smith's main entrance (College Lane) shortly after the fourth set. The Office of Admission is on your right, overlooking Paradise Pond. Parking is available next to the office or along Route 9.
From the North: From I-91 South, take Exit 20, and follow onto Route 5 south into the center of town. At the intersection of Route 5 and Route 9 (Main Street), turn right onto Route 9. Then follow the same directions as above from Route 9 to campus.
From the East or West via the Massachusetts Turnpike: Northampton is on Route I-91 North (Mass Pike exit 4). Once on I-91, follow the directions above for visitors from the south.
Or check out the Smith College website for other ways to get to campus (and incidentally, that's where the driving directions came from).