need E6320 eSATA driver for XP SP3

I have E6320 laptop running XP SP3 and want to use the eSATA port to connect my external backup drive. The eSATA port on this model requires the BIOS to set the SATA mode to "AHCI" in order to enable it. However, my internal HD will only boot with the SATA BIOS set in "ATA" mode. I have the latest Dell SATA drivers for XP that will install, however, they will not permit booting in AHCI mode.

The BIOS setup will find an external drive connected to the eSATA port if in AHCI mode, and it will see the internal drive as well, but it just won't boot. The computer boots fine in ATA mode, but cannot find any drive connected to the eSATA port, even from the BIOS setup.

Supposedly, driver R291722 from Dell downloads is the latest and will support XP, Vista, and Win7 and should allow AHCI mode. I tried installing this and it went about 90% through the install process before returning the error "This computer does not meet the minimum requirements for installing the software".

One of the more useful features of this Dell laptop is the built-in eSATA port, but as-delivered, it was not functional ... I have a "Catch-22" situation where the Dell hardware as-delivered needs an updated driver to allow everything to work to work as-advertised, but the updated driver Dell offers doesn't like the Dell hardware ???

Is there some 3rd party driver that would be a work-around for this? Thanks in advance for any ideas.