ESATA Problem Windows 7

Have you installed in BOTH Windows the latest pertinent drivers for the Marvel chip that provides the eSATA port on that mobo? They may not be the same for the two OS's. Check the ASUS website for them.

This provides an interesting question for setting up the BIOS. Win XP does not support AHCI mode for a drive unless you install its correct driver at the time of installing XP. Or, if the AHCI device is going to be used only for data storage and NOT to boot from, the driver can be installed in Win XP after it is running. Win 7 does have its own built-in support for AHCI. In your case, assuming your are NOT trying to boot from the eSATA drive, I would suggest you should have that port set to operate in AHCI mode and ensure the right driver for that port, including ACHI capability, is installed. It sounds as if that is in place for Win XP. But I'm not clear whether you have the port set to ACHI mode, which should be necessary to get hot swap capabilities in both OS's, or whether Win XP is succeeding because you already have a driver installed to provide that functionality independently of any BIOS mode setting. If the port is not or cannot be set to AHCI mode, that could be involved in the inability of Win 7 to provide the same functionality.