Don't know if i've done the right thing or not but i just finished upgrading my rig to a SANDY system and did a clean install of W7, formatted my fsx drive and left the default AHCI enabled in my bios.Both my drives are WD-CB-1T-7200rpm.

No, it's the other way around...the reg key edit will be required if the SATA mode is changed *to* AHCI mode and the AHCI driver is not enabled. The IDE driver pciide.sys is always enabled when Windows is installed, regardless of the actual presence of a device running in IDE mode. The AHCI driver msahci.sys, is only enabled at the time of Windows installation if one of more of the active drives is running in AHCI mode.At any rate, the registry edit in the referenced KB article only covers enabling the AHCI driver, and does not affect the IDE driver.

Perhaps that's the way it's meant to function, but in practice the effect is often the same. In my job as a PC technician (at a serious repair shop, you know, one actually interested in repairing PCs rather than selling you a replacement with a warranty) I have seen it many times when working on modern PCs that have Windows installed on a SATA drive which is configured to run in AHCI mode. Our HD diagnostic tool (MHDD) doesn't recognize drives set to function in this mode, so we have to go into the BIOS and change the SATA mode to IDE (or whatever the manufacturer has decided to call non-AHCI mode). Occasionally I'll forget to change the setting back to AHCI and on boot will get a nice 7b stop code. It works both ways, if you change to AHCI when the system was already configured to run in IDE mode, Windows will likely not boot. On Vista or 7 systems the startup repair utility can *usually* fix this.

My question has been answered!