fit woodstove into old fireplace?

I have a fireplace made of brick. I also have a cast iron wood burning pot belly style stove. I would like to put the stove into the fireplace insert. Anyone know how i can do this and if there is any reason i shouldnt?

You can. You will lose some of the efficiency of the stove, but, it can be done. It is WAYY more efficient than a fireplace, too! The key to doing this safely is to attach a chimney liner from the stove to the top of the chimney.
Stoves work on draw and not draft. If you merely vent the stove up the chimney, the exhaust rapidly expands and cools inside the chimney. This will cause a buildup of soot in the chimney and set you up for a fire. A fireplace works on draft. Draft keeps the speed of the exhaust gases higher (with much more heat escaping up the flue) and this keeps the soot lower.

You can get more heat out of it if you use a blower.