Page 40 of the included Installation Guide has a nice description, but I wanted to keep it in my online notebook for later.

Press F1 when booting the server to access the Bios/Configuration

Devices & I/O Ports
Advanced Chipset Control
Serial ATA

Parallel ATA: Enabled
Serial ATA: Enabled
SATA Controller Mode Option: Enhanced
SATA RAID Enabled: Enabled

Native Mode Operation: Auto -> Serial ATA
(dissapears when "SATA Controller Mode Option" is switched from "Compatible" to "Enhanced")

"SATA AHCI Enable" disappears when "SATA RAID Enable" is switched from "disabled" to "Enabled"

Save this configuration and run through ServerGuide. Pick the Express RAID configuration, but change the initialization from "Clear" to "Quick" if the drives are new and haven't been used before now to help speed up the process.

Reference page at IBM website with information on using "Quick" instead of "Clear" to initialize a newly created array. IBM