Take I-76 west to Harrisburg, PA. Exit on I-283 on the east side of Harrisburg. This joins I-83 North and US-322 West after a few miles. Take 322 from Harrisburg to State College. You will have interstate all the way to Harrisburg, then mostly divided highway from Harrisburg to State College, although there are some two lane sections that can be pretty slow (especially just west of Harrisburg, which is currently under construction and can be very congested). The entire trip should take about 3 hours from the Philly area.