Here is a vid on the P0442, but I don't think thats your problem. http://www.youtube.com/watch?v=lNI3RZXUSaM
I did not crawl underneath when I had the p0422, I could just hear the leak, I took it to a muffler shop, they cut out the rusted section and welded in a new 6 inch pipe. Upon restarting the car, the p0422 light went out. I don't know how to test a cat except for smell, bad gas mileage, lack of exhaust etc. How many miles on your car. I replaced both my 02 sensors at 120k miles. It could also an exhaust leak closer to the manifold too. If you have to replace the cat, they are really expensive and aftermarket cats won't work imho. I've read tons of posters who use aftermarket cats only to get more codes.
Whatever happens, please let us know how you resolve it.
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