All the D3 pie chart examples out there are pretty complicated and crowded with features you probably don’t want.  Here’s an example of one that’s pretty basic:  http://jsfiddle.net/ragingsquirrel3/qkHK6/.  I’m still working to make it simpler.

It’s based on this example:  https://github.com/mbostock/d3/blob/master/examples/donut/donut.html.