I've been trying finally get to grips with Blender over the last couple of months and have been trying to make a spring using the screw tool but have so far only been able to modify its diameter using the cursor. How do you modify the pitch of the spring and come to think of it constrain its diameter through the spiral. It seems that it always moves slightly outward on each rotation...

I have not used the screw tool much, but you might try out dupliframes. They are very simple to figure out and gives you much more control over your spring-like shapes.

http://www.blender.org/modules/documentation/htmlI/x9547.html