How can I add a circular prop?

[arrowmarcher]

I want to have a stage in my drill, shaped like a circle (5 yards in diameter, about 1 yard tall). When I click to add a prop it only allows me to make square props. I also tried to import a picture of a circle. When I did it still made a box and filled in the circle picture. I want to have performers on the stage, but the picture stays in the foreground and you cannot see the X that marks their spot. Please help, I can elaborate more if I wasn't descriptive enough.

[Pyware]

What version of the 3D are you running? Also what operating system are you running on?