I just installed a DP this past weekend... Its a very easy install; straight forward. It does take all day though, it took me 9 hours from start to finish; setup, cleaning up, etc... All you really need to make sure you have are mechanic gloves or you will end up gashing your hand to shreds, lots of extensions with wobbles, a couple of 14mm (medium depth and deep) sockets and wrenches. Oh, you will also need some penetrating spray oil for the manifold bolts and O2 sensor... And be extra careful with the O2 sensor when removing it...you will need an O2 socket... You have to apply penetrating oil to the O2 threads and loosen and tighten little by little. This is the biggest pain in the ass part of this job. You CAN NOT, absolutely NOT apply any force to the O2 sensor while loosening it. I followed the rules and slightly applied force and messed up the threads on it. Just loosen slightly, then tighten, just keep on working it until you get it off... If you mess up the threads, its a $400 replacement. DO NOT FORCE THE O2 even slightly... Everything else is cake... Make sure you also have a torque wrench.
Regarding the cats, I went with a catted DP because according to the vendors, a lot of owners have come back (4-5 months later) begging to weld in a high-flow cat due to the car's interior smelling like gas!!!
Good luck and take your time!!! (2thumbs)