I'm using a scsi disk for my system and cache partitions, and an IDE disk for bulk storage. Everything installs just fine using the instructions for SATA. Even the device names are the same: /dev/sda1 is my root partition.

However, when I go to boot off the hard drive, the kernel attempts to mount root as ext2 instead of ext3, and says

Cannot open root device "801" or unknown-block(8,1)
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(8,1)

Ext3 supprt is compiled into the kernel, and we can obviously read the scsi drive, at least enough to load up the kernel and do a bunch of crap.

Any ideas?

Are you sure that ext3 is compiled in the kernel or is it a module? The same applies to your SATA controller. It seems to me that the kernel doesn't support it on it's own and needs a module. This module resides on disk but there is a chcken and egg problem. You'll need an initial ramdisk with the proper modules or a kernel with the ext3/SATA support built-in instead of a module.

According to the config file in /boot, ext3 is compiled right into the kernel.

I'm not using SATA, I'm using a motherboard with an Adaptec SCSI chip. I'm thinking the system can see it just fine if we are able to boot with the kernel off the hard drive.

Ah I see I didn't read your post properly. Now could it be that when you boot off the harddisk that the IDE disk that you use for bulk storage is detected first and is assigned /dev/sda because of SCSI emulation? This would make your SCSI disk /dev/sdb or the like. This can usually be circumvented in the BIOS or by passing kernel options. Or you can change /etc/fstab and make /dev/sdb1 the partition with the rootfs.