Excellent write up. I did this slipsream the other day, but just now came across this post. I am running one drive, but trying to run AHCI mode and install XP Pro. Before slipstreaming, It would not detect the drive of course. I slipstreamed the drives exactly how you have in your guide, the only difference is the source cd was not a clean one, but a disc I slipstreamed SP2 in a few months ago. Does this matter that it was an nlite created disc even though the only thing changed was slipstreamed SP2 in? OK, so here is my problem. The slipstream must have worked, becuase it recognized the drive during setup, I created and formatted a partition, and sucessfully copied all of the XP setup files to the BRAND NEW hard drive. Just before the reboot, it says cannot copy file Uknown.sys and lets me canel or skip. Next, it reboots your computer to finish the install. It reboots, but after the POST screen, it reboots again and continues this reboot cycle. Any ideas? This computer was working fine with exact same configuration before I RMA'ed the drive, so I know it's not the bios or connectors or anything. From reading around, it looks to me that it loads the controller driver during the initial start, allowing my SATA drive to work, but then it will not copy the driver to the hard drive, not allowing it to boot. I don't know what Unkown.sys is, but others have the same problem, only named different things .sys I loaded used the drive as a slave an loaded up with my Vista drive and copied over the files iastor.inf iaahci.inf and iastor.sys over to the new hd that has the preinstall files copied on it into the i386 folder. No dice. Still does the same thing. Any one can help?