it's in Pisa......
Sorry, cheap shot that was. The airport bus stops outside the beautiful enclosed square that the tower stands in, with the cathedral and baptistry. This is to the north of the river, and just south of the dual carriageway ring-road (if you look on multimap or google).
A lot of 'modern' Pisa goes on to the south of the river but is nonetheless interesting. This is aso where the railway station lies.
The distance between the railway staion and the tower is possibly just about more than you want to walk and still have energy left over for site-seeing.