It sounds like you have two different problems. If the blower motor is only working on high, then most likely the resister is bad.
If you are not getting heat, there are a couple of things to check. Is your temperature gauge showing that the vehicle is warming up? If not, there could be a thermostat problem. If the gauge is reading that the vehicle is warm, then it could be a blend door issue. This means that when you are putting the vents in heat mode, they may not be opening to let heat into the vehicle.
The other issue could be that your heater core is not getting coolant sent to it, there could be a clog somewhere.
I would start with these things first and work from there. Good luck.
〉 Answered on Nov 20th, 2007 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines