Tax information for international students can be found at  www.upenn.edu/oip/isss/tax; as noted at this web page,

“In general, international students and scholars in nonimmigrant visa classifications must pay city, state and federal taxes if employed by the University of Pennsylvania.  However, in certain instances they may be exempted because of tax treaties between the United States and their home countries, or if their employment can be considered a fellowship, as defined by the IRS.” 

Funded students are considered University of Pennsylvania employees.

Tax treaty information can be accessed @ www.irs.gov/businesses/international/article/0,,id=96739,00.html

The University of Pennsylvania of Pennsylvania Corporate Tax Office provides information re: funding & graduate students @ www.finance.upenn.edu/comptroller/tax/prizes.shtml