10 days isn't a whole lot, depending how you like to travel. Two ways to go. Use Salamanca as the base, and take side trips. From Salamanca you can do easy day trips via bus or train to: Avila, Zamora, even Segovia.Also, Ciudad Rodrigo. Cooold that time of year in Castilla. Check out the great bancotel.com deals in Salamanca: the Rector is fab (a few others, too, but some to be avoided. check with the board). For this kind of trip you don't need a car. If you like to drive, tho, then you are best served w./ an itinerary like: Madrid to Salamanca, spend a few days there, then on to some of the cities mentioned, cross over into Portugal (Lisbon is a bit far but you could make it)...You do NOT need or want a car in madrid, salamanca, etc. If you have one you'll only be parking (and most likely paying for parking!). If you plan to spend some time in madrid, do it before/after you pick up the car.

Check out the parador.es deals, too, under 5 nights, special packages. 2 summers ago i did Madrid-salamanca-whole bunch of towns in extremadura and castilla-back to salamanca to pick up son studying-back to madrid. it was awesome, if a bit TOO MUCH.

saludos