Changing SATA/IDE to SATA/AHCI in BIOS

I have a MSI K9A2 board with AMD 8650 and 500gb Samsung HD501LJ + 64GB WDC WD6400AAKS SATA-HDs working on Sata controller. I have also got a LiteOn dvd writer and TDK CDRW321040B CD-RW on PATA controller and am running Windows XP with Service Pack 3 on this computer. At the XP setup I put Sata mode to IDE in bios because there was no where anything like legacy mode or AHCI. I think that I cannot use an external SATA disk as IDE mode since it does not support plug and play like usb? So, I want to use a eSata connection for my 1TB eSata hard drive as I have both eSATA and USB casing and it will be faster as well. So I was wondering that if I change the SATA mode to RAID then will it give me AHCI function like plug and play? Thanks for any information.

As per the MSI website and its manual for the board that you have, the raid controller is "AHCI Compatible" that means the driver is an AHCI one. Since intel uses AHCI driver for their Raid so it is possible to get your plug and play that way. You can also try to find some information on SB600 on google and check what others are experiencing with that chipset, search for “ATI AHCI Compatible RAID Controller -x86 platform”.

http://eu.msi.com/service/download/manual-6515.html

You can also try to buy a PCI Express x1 ESATA card, as an alternative solution.

I think that with your MSI motherboard there should not be any kind of issues by re-using the external SATA HDD with eSATA connectivity. The motherboard that you have is not having an eSata port, so I think that you will be using an eSata adapter affixed to the backplane of the desktop computer case that you are using. And the Sata data cable will be connected to the adapter that will be connected to one of your motherboard's Sata connectors.