Well, my mapping software says to take I-81 To the PA Turnpike Northern Extension (I-476) to Philly, then hop on I-95 and get off of it in Florida on I-4 to Disney.
I disagree. Coming out of 'Cuse you're looking at hitting Baltimore right at the beginning of rush hour, and even worse, having to deal with the DC Beltway. If you want a much smoother ride (and by smooth, I mean traffic, not roadways), I'd suggest taking I-81 to I-77 in southern Virginia and taking that to and through Charlotte to South Carolina, and hopping on I-26 to I-95 and continuing on down.
Believe me, staying away from the East Coast Megalopolis is going to save you a bunch of head aches.
Time comparison. First option: 20 hrs, 16 minutes. Second option: 21 hrs, 4 mins.
And if you have a laptop, I'd recommend picking up Microsoft Streets and Trips with the GPS transponder for your trip. It's awesome. I use it for work all the time.
Cheers,
Dave