Or paint.net which I have played with and liked, but at the time had no transparent png support. (Now it does).
Also, you need to install the M$oft .NET giant bloatware framework monstrosity, but many people already have that installed.
But, FWIW, I agree with Don and Ravs - Try the GIMP (It is what I primarily use) and it supports tablet pressure sensitivity (which paint doesn't )
-Rob A>