[bepperb]

I have an 04, so I can't say for sure, but at least on ours the first catalytic converter is the same thing as the exhaust manifold, which explains why the manifold costs 450 bucks at toyotapartscheap.com. I might email them to verify that this is the manifold/converter, and buy it there. You'll also need a new exhaust manifold gasket, a can of PB blaster, and an impact wrench or a good length breaker bar (or a cast iron pipe over your ratchet).

I'm not sure how to determine which cat is bad, sorry. But, from the manual it doesn't appear that there is an O2 sensor after what looks like the second cat. So my assumption would be that it's the first.

The actual name on the diagram is "Exhaust Manifold Converter Sub Assembly". If you want some .pdf's, I can email them to you.