Good question. I was digging around earlier, without much success. I seem to recall, but have not been able to find a source, that the Dem to GOP numbers the past two Presidential elections were nearly dead even in 2004 and +2-4 Dems for 2000. But the only thing I've been able to find so far was voter registration in Nov 04 showed Dems leading Pubbies about 48-41.
I'm hoping some of the PA residents can answer your question better than I can.
Here's an answer, finally, from Jim Geraghty of National Review. D-41%, R-39%, I-20%
And the ARG used a +14 Dem sample. Not particularly realistic, and McCain's still only down by four!