Here’s a good read from security analyst/guru Mike Rothman on how penetration testing can help with compliance.
The only thing I’d add is that you’ve gotta do more than traditional “pen testing” as we know it. And you’ve got to do it periodically and consistently. Not just one time. Use what I call the ethical hacking methodology that combines the best of penetration testing and general vulnerability testing. When seeking reasonable security, look far and wide at weaknesses in technical systems and IT operations. Problems are abound in both areas. Then…as a nice side effect, if you do your security testing the right way AND follow-up and plug the holes, you’ll achieve compliance with practically every law or regulation known to man.