I have that problem and the simple solution is to let the Win7 DVD extract all the files to the HD after which it will do it's first reboot. This is when you changed from IDE to AHCI. Simple and effective. 
Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn!
"The sky was the color of a TV tuned to a dead station" - Neuromancer