Argh!

So, I have this geometric figure I want to draw on my computer. It consists entirely of circles in proportionate sizes. This exercise would be downright trivial in Geometer's Sketchpad...if I had it. Since I don't, I'm looking for recommendations of programs that are free-ish that are a) precise enough to let me draw concentric and relational circles with proportional (a, 2a, 3a) radii but are b) simple enough that I can use without tutorial from another human being or trolling the internet for forums and help files.

shogunhb for the Win!

Google's new thingy is exactly what I was looking for. Now I just need a way for the parts outside of the round to show up as translucent instead of white. Ideas?