Question
I am not sure how the critter got in the house.  I heard something Friday night May 2, 08.  Opened the door and there was a approximately 20 lb. raccoon in the doorway eating my cats food.  The animal seemed not to be scared by my blood curdling scream.  He has been down in my basement since Friday. This morning I looked and the screen to the fireplace had been thrown across the room and none of the food I put out was gone.  Help

Answer
There are so many things that you need to consider to respond to this matter, I must simply refer you to a variety of web pages.

http://www.icwdm.org/diseases/raccoonroundworm.asp
Most people are aware of rabies but few know of the roundworm threat.

http://www.icwdm.org/handbook/carnivor/Raccoons.asp to learn how to capture them.

http://www.icwdm.org/Inspection/Default.asp   ON this  page, you will find a link to inspect your home so you can figure out how he got in.

http://www.icwdm.org/VendorsService/default.asp  Tips on finding a qualified expert.