FDxc

hi.
I have a problem.
I think this is a cat problem but i am not sure.
I have this part in the middle of the car- (right behind the muffler and y pipes) (that is the cat right?) well that and the piece right in front of it are both rusted. The one in the front has a hole in it, and i think thats why it keeps on smelling. Do you have some advice on what it is and how i can fix it? How much are we looking at? I have pics of the problem if that'll help.
Thanks
HERE ARE SOME PICTURES !
http://www.geocities.com/fc3sxc/problemleft.jpg

and

http://www.geocities.com/fc3sxc/problemright.jpg

PLEASE HELP ME OUT.
thanks! (where can i get a replacement?)