BTW, I did a bit of research, and it appears that you can put the ZHP suspension underneath your car for about the same price as a Dinan Stage 3 -- about $2000 or so.
Performance package changes (from 330 Sport) include:
Springs are 0.6 inch shorter, 6% stiffer in front, 8% stiffer in back.
Front shocks 50% firmer in compression, 35% firmer in rebound.
Rear shocks 20% firmer in compression, 8% softer in rebound.
Anti-roll bars are 0.5mm thicker.
Bushings are more rigid (no more detail)
From Bimmer, November 2003, page 50
Type 135M Performance Package wheels from BMWWheels.com:
$412.00 FRONT $420.00 REAR plus the freight to your door.
Bridgestone S03 from TireRack:
225/40YR18 Price: $184
255/35YR18 Price: $226