Maths will help. I've tasked a bunch of people to get the graphics system to draw circles. But I haven't heard from any of them since. So it's your job now.
Get
FX Composer and load up the graphics.XNA solution. Your task: write a pixel shader that can draw a circle given a quad (see the shader for drawing squares for reference). And integrate it in to the graphics code.
Alternatively: get Graphics.GDI set up to draw quads like Graphics.XNA can. GDI is the internal drawing routines that C# has for winforms. I don't think there's even a solution or project set up yet. Use the ones for XNA as a starting point.
The code is not concrete here at all, so feel free to massage it to make things easier to work with.
That's a rough outline. If you need more direction, we can set up a skype call after work. Do you have skype? If not, grab it. It's basically a way to do phone calls over internet for free. If you don't have a mic, that's fine. I just don't want to have to type this all out again. What time zone are you in?