Hi backpacker, if your only there for 2 days I'm presuming that you won't have to much luggage with you ?, if so you can easily catch a bus very close to where you are staying for I seem to remember 1 euro each the bus stops outside arrivals at the airport and does a circular route around Pisa it stops at the railway station aswell, with regards getting to the station you can either catch the bus again, or if you are feeling energetic it is easy to walk to, you cross The River Arno at the Ponte Mezzio and walk in a straight line down the Corso Italia and you will be there in about 15 mins or so, there are plenty of trains to Florence which in Italian is Firenze, I'm presuming again that you are going to see the sites of Firenze The Duomo, Ufizzi, Ponte Vecchio etc if so you need to get off the train at Firenze Santa Maria Novella ( Firenze SMN), but word of warning, be very carefull at railway stations in Italy inside and out as there always seems to be very dodgy looking people hanging about outside normally gypsies, druggies, beggars, alcoholics or just general dodgy looking people so mind your wallets and don't be taken in by gangs of children wanting to make friends with you as they will be trying to nick your wallet, if in doubt use this phrase which always works for me "Mi lasci in pace pronto" which means in Italian "leave me in peace immediately" works every time, enjoy your trip.
Buono fortuna
Sliema2