No worries DJB, you see with computers/electronics etc its the whole case of rubbish in-rubbish out.
So unfortunately the information you get back from the community depends on the amount of information you are willing to put in.
So if you post a vague request without going into exact details then you can't expect anyone to assist you because there are too many variables for anyone to assist you with a solution and there are many potential solutions to your problem without knowing the specifics.
So you need to give some more detail, like the type of RC car, the type motor (brushless or brushed), voltage and current ratings etc etc. What exactly do you want to control speed? Also what is in the car does it have a speed controller in place already or do you want to directly control the motor etc etc.
I don't think anyone is being hostile its just that many people here put a lot of time into helping others and it gets irritating when people just want solutions handed to them on a plate, and there is google for that anyway.
Hope that helps.