Grab yourself a pair of ebay headers from a trusted seller, and loose the restrictive stock muffler and you should be good. It's a cheap setup that gives you a beautiful exhaust tone and isn't too raspy. Your not going to gain much power by going full exhaust if you have headers and a different muffler.
2000 328i 5 Spd Black on Black
FS. JB Racing Lightweight Flywheel (Non-M 6 Speed ONLY) - $450 obo
FS. Spec Stage 3 Clutch Kit (Non-M 6 Speed ONLY) - $400 obo
Dinan - Remus - UUC - Koni - AC Schnitzer - VMR Wheels - Brembo - Bridgestone - Umnitza - Bimmer Evolution - Tischer BMW - WeissLicht - Alpine - Rockford Fosgate