It's an amazing engine... and not too much in common with NASCAR... but one thing the M3, and virtually every piece of American iron, do have in common is a cross plane crank. I found some good pics here if there's any question on this one:
http://www.kenrockwell.com/bmw/m3/2007/engine.htm
A flat plane crank would give the sugary sweet Ferrari-esque / F1 / Champ Car / etc. ripping sound, but it comes at the cost of increased vibration, so is probably out of the question for a BMW production car. Physics is conspiring to make the M3 sound like a Vette and there's no way around it! Damn.