I have the ASUS P4C800-E MB Deluxe and a WDC 250 GB SATA Disk Drive.
I am running Windows XP Pro SP1 with the ASUS Motherboard's BIOS Revision 7.
I want to achieve the fastest performance possible so I connected the WDC 250 GB SATA Disk Drive to the ASUS Motherboard's onboard Serial ATA ICH5R Connector to obtain the 150 MB Data Transfer Rate.
The onboard Serial ATA Interface is faster with the 150 MB Data Transfer Rate then the onboard Promise PDC20376/78 RAID Controller that only supports the 133 MB Data Transfer Rate.
I plan for now to have only one SATA 250 GB Disk Drive in the Computer.
In the IDE Configuration BIOS Setup Screen I have the following settings.
Onboard IDE Operate Mode - [Enhanced Mode]
Enhanced Mode SUpport on - [S-ATA]
Configure S-ATA as Raid - [No]
Serial ATA Bootrom - Disabled (This Field Only Appears When The Item Configure SATA as RAID is set to Yes)
IDE Detect Time Out (Sec) - 
Is there any performance or reliability advantage in setting the one WDC SATA Disk Drive in a RAID 0 Configuration using the RAID Feature of the Intel ICH5R Chipset, then leave it in the non-Raid Configuration that it is now?
Another System Problem that I have is the Found New Hardware Wizard the "WinXP Promise SATA-378 IDE Controller" keeps popping up.
When I install the Device Driver Software, it tries to load the "Ulsata.Sys" File from the "ASUS" System Software Support CD-ROM Disk from the following Path "\Drivers\Promise\378ata\winxp".
When it is finished I receive the System Error Message
"Cannot Start This Hardware"
"There was a problem installing this hardware:"
"WinXP Promise SATA378 IDE Controller"
"This device cannot start. (Code 10)
I tried this procedure many times and the "WinXP Promise SATA-387 IDE Controller" will still not load properly.
Any ideas why the Device Driver Software for the "WinXp Promise SATA-387 IDE Controller" will not load?
Since I am not using it should I just disable the Promise Disk Controller in the Motherboard BIOS, or try to obtain the Software Device Drivers from somewhere else?
Have you already created a RAID Array? Were you able to install XP yet? If not, I'm pretty sure that you will have to create an array first by, I think the combo is, Ctrl - F after POST. Create a RAID 0 and then the OS should be able to pick up the drive. This is if you are using the SATA connectors on the mobo. SATA doesn't really have much to do with the bios settings below with the exception of the boot order. Also, are you getting the device driveers for ASUS site? Do not use the ones from Promise as each mobo manufacturer modifies the drivers for their boards.