I experienced the same issue with the Asus P4S800D-E Deluxe yesterday. It took some extensive digging to find the answer, but here it is.
First, you will need an SATA RAID driver to perform the installation. The problem I had was related to woefully inadequate instructions from Asus. It seems a bit odd that a RAID driver is required for a non-RAID installtion, but that is probably due to the nature of the SATA controller on the SiS chipset.
Using the motherboard CD, navigate to Drivers/RAID/SiSRAID/DriverDisk and click on MakeDiskEXE.exe. This will insruct you to insert a blank formatted floppy disk in the floppy drive. It will then create a driver disk for use in installing your operating system.
Next, begin the installtion process from the operating system CD. Press F6 as sson as the process begins so that you can instruct the installation to use the driver disk for the necesary driver. In approximately one minute a driver setup window will appear. Press S to load the driver from the floppy disk. Insert the floppy disk and press ENTER. You will then see four possible driver choices as follows:
WinXp SiS964 RAID Controller
Win2000 Sis964 RAID Controller
WinXP Sis180 RAID Controller
Win2000 Sis180 RAID Controller
Depending on the operating system you are installing, choose either the WinXp SiS964 RAID Controller or the Win2000 Sis964 RAID Controller. This is the correct driver for drives attached to the SATA1 and SATA2 connectors on the motherboard. After you have made your selection, press ENTER.
Once the driver has loaded from the floppy disk, press ENTER again and continue with the operating system installation as usual.
This should get you up and running.