To generate an interactive map of the town/area just go to www.virgilio.it or mappe.alice.it and write 'siena' in the field labelled 'citta`', optionally you can add the address in the field 'indirizzo', eg 'val di montone' '1'if you want to go to the conference hall.
To find your path eg in Siena, scroll down to the bottom of the previous page and you find 'calcola un percorso partendo da/per raggiungere', click on it, fill the address in the fields of the new window, click on 'pedonale' and on 'crea il percorso'.
Siena is a small town and distances are usually short. If you arrive by train, there are several buses stopping in front of the train station which will take you close to the town centre. The price of one way ticket should be less or equal to 1 E. Timetables can be found at TRA.IN . If you arrive by bus, the bus terminal will be already close to the town centre, eg Piazza Gramsci if you come from Rome or Via Tozzi if you come from Florence.
A taxi should not be too expensive because distances are short, typical prices can be found at the website of the Comune clicking on 'tariffe'. On the other hand circulation is often very slow and unless you have heavy luggage, it might even be faster to go on foot.