I managed to dig out the MoB user guide.
Following is what is written in the guide:
1. "JMicron IDE connector (40-1 pin PRI_EIDE [black])
This connector is for Ultra ATA 133/100/66 signal cables. The
JMicron IDE connector supports up to two IDE hard disk drives for
easier storage. This connector does not support ATAPI devices."
Taken from Page31 (59 of 212).
http://dlcdnet.asus.com/p
ub/ASUS/mb/socket775/P5W%20DH%20Deluxe/e2557_p5w_dh_dlx.pdf
The two IDE HDDs is currently connected to this
by using the JMicron PCIE to SATAII/IDE RAID Controller and they
run fine.
2. "Intel ICH7R IDE connector (40-1 pin PRI_IDE)
The onboard IDe connector is for the Ultra DMA (133/)100/66
signal cable.There are three connectors on each Ultra DMA
133/100/66 signal cable: blue, black and gray. Connect blue
connector to the motherboard's IDE connector, then select one of
the following modes to configure your device.
Install devices on this connector (PRI_IDE) first, then install
on the JMicron IDE connector, PRI_EIDE".
Taken from Page32 (60 of 212).
http://dlcdnet.asus.com/pub/ASUS/mb/socket775/P5W%20DH%20Deluxe/e2557_p5w_dh_dlx.pdf
The two IDE DVD drives are connected to this connector.
Sorry, I do not know how to paste the PDF image from the online
manual.