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.
'02 ///M5 Imola Red / Imola Red '09 335i Alpine White / Coral Red
'04 E55 AMG Brilliant Silver / Anthracite
'96 318i Alpine White / Black
'01 330Ci Titanium Silver / Coral Red
'96 328i Jet Black / Black