Yes, I have an idea, but you're not going to like it, because it's horrendously complicated and hard to get right. Create a Windows PE (or BartPE) boot CD containing the correct SCSI drivers. Boot from that, confirming that you can see the SCSI device OK. Then do an unattended install from the hard disk. You'll need to copy the Windows XP CD to the disk, slipstream any drivers/service packs/hotfixes into the image (or you can put them in a separate directory and set up unattend.inf to pick them up).

It's horrendous. It's quite slick once you get it working, but it's usually overkill for a single PC (you'd generally capture the image and then use something like ADS/WDS/Ghost or a disk duplicator to slap it down onto multiple PCs).

Alternatively, you could try booting from an SP2 slipstreamed image. Maybe that'll be more reliable, or even have the drivers in it.

Ooh, I've had another idea. The SCSI controller's not on the other side of a PCI-PCI bridge that you don't have drivers for during setup? Sometimes manufacturers do this because they've run out of PCI devices on the included southbridge. Not sure how to get around that one.