Also that downpipe is $436, you may want to check out zzperformance for a better price (I believe around 240 or 250 for a 3 inch ss bolt in with cat, less than that for the non stainless). I'm hopefully getting a downpipe this spring, so I don't know quality or anything, but lots of other guys here know a lot more than I do.
Just like Hutch said, if you're looking at headers most come with their own downpipe.
_________________________
1999 GTP, 105K
Alpine w/ Bose, HUflushmount, volt booster/alt rewire, summit muffs, ss tips, CAI, 180*, ZZP 1.0 PCM, SE Rims, D/S Rotors, some cool gauges