XP 64 bit will not install correctly directly from the Windows Disk.

A driver disk for the NVidia disk controller is required.

Download the latest drivers Nvidia drivers from Nvidia’s website.

My XPS 720 used an NVidia 680i chipset but use the correct drivers for you motherboard.

Create a install floppy to be used during the Windows installation.

1. Extract the drivers
2. the extracted directories should contain the following
   …\IDE\WinXP\sataraid
   …\IDE\WinXP\legacy
   …\IDE\sata_ide
3. Copy the files from either the staraid (if you are using raid) or
   form the legacy (if you are not using raid) to the floppy

Boot your machine with the XP 64 installation CD/DVD

During the boot you will need to press F6 when the message to install additional drivers appears at the bottom of the screen (best to have the floppy in the drive from this point).

The install will continue for a while and you may not think you hit F6 in time but dont worry, a message should appear.

When you are prompted press ‘S’ to specify the additional drivers.

The disk should contain 2 drivers:

NVIDIA RAID CLASS DRIVER
NVIDIA nForce Storage Controller

Both of these will be required if RAID is enables.  Select the first one and once complete press ‘S’ a second time and select the second one.

If you are not using RAID on the nForce Storage Controller will be required.

The installation should now complete correctly from the Windows XP disk.

Here are links to the info I found on the NVidia site:

NVidia Drivers and NVidia RAIDF6 readme file