I am using Adobe Photoshop Elements but I think most of the tools will provide the same feature-set. Adobe calls it a "circle tool" that allows me to cut out a circle of a fixed size.

I seem to remember PSP having the same feature when it was owned by JASC. I don't think they would have removed it. But Paint Shop Pro is available for a 30-day free trial download from Corel. Same with Photoshop Elements -- that's probably the best way to try it out and see if it works for you.