Cadillac Repair: Head Gasket or Water Pump, signs of a blown head gasket, blown head gasket

Question
I have a 99' Cadillac Deville and i can't figure out weather my head gasket is blown or my water pump is bad.  I can start the car up with no problem and it only overheats when i drive a certain distance.  When it does overheat it leaks anti freeze from the water pump.  I took it to pep boys and they said it was something internal. But yet the vehicle shows no signs of a blown head gasket.  It blows very little white smoke out, and it is not mixing oil and anti-freeze, and does not shoot it out when the car starts, and the car starts just fine.  What could be the problem or reason it over heats?

Answer
Eric,
The car needs a more seasoned pro than you're likely to find at places like a Pep Boys, sorry.
A minor head gasket leak can still be found by "proper" diagnostic procedures. They'll want to check for exhaust gases in the water jacket, excessive cooling system pressurization, etc, etc.
Head gasket leaks drawing coolant in can sometimes be fixed with a stop-leak treatment but I'd warn against excessive use of those products since they can clog all kinds of other things in the cooling system.