Bricks, Masonry, Asphalt and Concrete - Round brick planter?

I am toying with the idea of building a round brick planter around a grown tree on my front lawn. I would plan to build bricks in a circle around the tree 1-2 feet high, then fill with dirt and plants, etc.

I have never done a brick project before ... how hard is doing a circle? Does anyone have a good link to a site discussing how to make circles out of brick? If I do this, how to determine how many bricks I need? Or is this definitely not a DIY project?

P.S. I really want to use traditional bricks for this and not another paver/material type as it would match the bricks on the exterior of my home.

Thanks for any help/hints you can provide!!!

Here is some information regarding adding dirt around trees.

http://www.wvu.edu/~agexten/hortcult/treeshru/treewells.htm

Hope this helps.