What are you trying to change with the software? Just new stock stuff? If so, I doubt there's anything noteworthy to be had with the NA motor.
Try contacting the guys over at Stance Factory. They can do pretty much everything under the sun when it comes to software customization.
Imola Red / Imola Red ///M5
E60 SSK, Dice iPod, Illuminated ZHP knob, MKIV, Euro Armrest, GT ExhaustDaily:
BCR Coilovers, 19x10 + 19x11 Rial Daytona Race, Michelin Pilot Super Sport
'04 E55 AMG Brilliant Silver on Anthracite
'96 318i Alpine White on Black
'01 330Ci Titanium Silver on Coral Red
'96 328i Jet Black on Black