you will have to change the boot settings to AHCI/RAID (from f10).
Once the machine has booted up, you will then need to got to the intel website and run the "autodetect for Driver updates"
You will then be given two updates, one for the Chipset (I think this is the ESB2) one and secondly the Intel Storage Manager which allows you to manage the RAID array in windows.
Be VERY careful of Windows updates though as I have seen these trashing your RAID array and sending you back to the start.
The name of the SATA controller driver has changed a bit from the early days to more recently, but in both cases ESB is in the driver name. I have updated a significant number of xw6400 workstations to the latest Intel available ESB drivers that I have located, and I do provide those drivers for download (both 32- and 64-bit versions) on the HP forums from a couple of days ago. Those two zip files provide you the initialization and install files that you would use to do a F6 floppy driver install during boot, but the initialization file can also be navigated to via Device Manager in both XP and W7, and updated in the usual way via that path.
Intel advises to use the initialization file that gets you both AHCI and RAID drivers for that SATA controller (to keep your options open), and that is quiet easy..... choose the "iaStor.inf" initialization file for your 32- or 64- bit operating system during your update process. I have added the step by step example of how to do that for those who don't know, on the HP forums, and you can find that via the second link below. For a time I seemed to be able to shift back and forth on my W7 installs between using the iaStor.inf and the iaAHCI.inf, but I seem to have lost that capability now. The iaStor.inf choice is all-inclusive, so that is fine.
These latest drivers are vesrion 10.1.0.1008, with driver date 11/6/10. Note that you should have BIOS set to "RAID + AHCI", and also should have the latest BIOS installed (2.38, from a Google search for "xw6400 drivers" and go to the hp link near/at the top of the list that shows up). These same drivers work for the xw6600, the xw8400, and the xw8600.
If you are still using the HP clone OS build that came with your xw6400 workstation from the factory you'll have an older version of that driver already on your boot hard drive, and you can update it with this latest driver via Device Manager, easily. I have done this update on every xw6400, xw6600, xw8400 and xw8600 I have tuned up (both XPPro32 and 64, and W7Pro64) and the drivers works fine.... that's over 20 workstations now. Of interest, there are some indications that this version of the driver, or later, may be necessary to allow those workstations to fully see a 3TB hard drive as a data disk (GPT format needed). I have not done that experiment yet, but that tidbit came from Seagate's web site on 3TB drives.
If you have a clean install of XP you needed to use the F6 floppy method (or equivalent) during that install, with BIOS set to RAID + AHCI..... In contrast, W7 and Vista have that driver on the install DVD but will only transfer that onto your boot drive during a clean install if you have "RAID + AHCI" set in your BIOS during the install. You can retrospectively fix a W7 install if you did not do that properly during the initial install...... you cannot fix that in XP (need to reinstall properly with floppy attached, sadly, if that is the case).
Here is one of my posts regarding this from the HP forums:
Here is another link to the post that includes more details on how to update to the most recent driver using Device Manager in XP and W7. This technique allows updating the drivers from a F6Floppy download, without using a floppy drive. Make sure to properly choose the zip file for either your 32-bit or 64-bit OS, of course. These work for me in all 32-bit and 64-bit versions of XPPro, Vista, and Windows7:
Here is the Intel download link for those latest drivers for the ESB2 chipset, for the xw6400, xw6600, xw8400, and that xw8600. Have been using them for over a year now, with excellent performance. I have searched many times for a more recent official version of the RST drivers that include the ESB2 chipset ones but these seem to be the latest. This link gets you to the 32 and 64 bit versions, plus the GUI installer for this version of RST.