enabling AHCI after installing vista or windows 7

In the bios there is a setting for which mode your sata controller operates in and there are some benefits from setting that to ahci.  I tried this bios setting (after windows was installed) and windows would no longer boot (not even the windows 7 boot repair utility could fix it).  Googleing the issue was not very helpful as most forum posts are moaning about how to find the right ahci driver.  But windows 7 (and I believe vista) are supposed to support ahci out of the box (ie they have the driver as part of the default OS).

So anyways I finally found an explanation in http://support.microsoft.com/kb/922976 that even though windows has the “boot” driver, it is disabled (as it is unused during the install).  So edit the registry and enable the boot driver… but it still doesn’t work for me. 

Though I’m not exactly sure why the default win7 boot driver wouldn’t work when enabled, I did manage to figure out that my ahci driver seems to be referenced in HKEY_LOCAL_MACHINESystemCurrentControlSetServicesamd_sata and setting the “start” entry to be “0” fixes my problem.

I’m guessing that if you install updated vendor drivers, they supersede the msahci driver, and thus one would need to enable those vendor ahci boot storage drivers.  But it seems like it should be easier that all this.