Final approach into the airport?

When planes are lined up in the air on approach for landing (either general aviation OR airliners,) obviously they need to keep a safe distance. My Question is: Does Air Traffic Control advise pilots what airspeed to maintain? Or is that the sole discretion of the pilot? ...Second Question: when Pilots on approach vectors are advised by ATC of altitude changes and heading changes, are these directions given by ATC people in the airport control tower? Or are these directions given by a separate ATC radar facility. In otherwords, is my umption completely wrong, that controllers in a control tower give orders that are limited to merely clearance for landing, and clearance for takeoff? final question: Are any of you familiar with the ATC function in the Microsoft Flight Simulator X DEluxe version? How does that work out? Do the simulator enthusiasts know what they're doing, with regard to the air traffic control function? are there any recommended books?