The map How to get to Purdue gives a good overview of town and how to get into town from the highway. But don't follow the directions given there, they'll get you to the stadium. To get to the Computer Science and Mathematical Sciences buildings, the directions below are easier to follow.
From Chicago: Take I-65 south to West Lafayette exit 178. Turn right onto State Road 43 South and proceed to State Road 26 (the second traffic light from I-65). Turn right and follow St Rd 26 (aka. State Street) onto campus. At the fourth traffic light turn right onto University Street. You can park in the University Street Parking Garage (called PGU in the maps).
From Indianapolis: Take I-65 north to State Road 26 exit 172. Turn left and follow St Rd 26 onto campus. University Street is at the sixth traffic light after you pass the Wabash River. Or you could just follow the directions for coming from Chicago, that's a bit farther to drive but it saves you a dozen traffic lights.
To MATH-175: The building right across the street from the parking garage is the Computer Science (CS) Building. The Mathematical Sciences (MATH) Building is the building with the breeze way underneath southeast of the CS Building. If you zoom in twice on the Campus Map Browser, you'll get pictures of the CS and MATH buildings. The workshop will be in MATH-175, which is on the ground floor in the northern part of the building.