HELP: 2000 TL HP gain

I have a friend who just baught a 2000 TL3.2. He wants to know what he can do to gain horse power without effecting his warrenty. I'm guessing a cold air intake, whole new exaust system. Let me know what you know and give me some suggestions on the best brands or brands you've tried and people who sell TL parts. As I said, I'm a little ignorant because I dont own a TL myself.

Intake and headers are a great start. The stock exhaust from the cat back is pretty low restriction already, you won't gain much with an aftermarket set up (which aren't cheap either).

AEM and Injen make several high flow intakes for the TL. The exhaust manifolds are definitely the most restrictive part of the TL exhaust; Comptech, OBX, Stone Racing, Megan and AlphaWerks all offer headers for the TL.