I am the happy owner of an AR31M, which came pre-installed with Vista. The story below explains how I managed to downgrade it back to XP Pro (UK) and got all devices to work: RAID, S-ATA, Video, Bluetooth, sound, camera, network, etcetera.
What you need before you start:
- The AR31M (in my case with 2x 100Gb S-ATA Hitachi drives)
- An XP Pro full pack installer CDRom
- The AR21M XP drivers
- The AR31M Vista drivers (for the VCC4 camera only)
- A USB floppy disk drive for accessing the RAID & S-ATA drivers during the XP-setup (unless you dare to follow this instruction)
- A floppy disk with the RAID & S-ATA drivers, here's the one I created.
- The NVidia unified GeForce Go driver plus the corresponding *.inf file from http://www.laptopvideo2go.com to make it recognize the AR31M's 7600 version. Here's the one I used.
- Patience.
Assuming a clean install, make sure you've backuped all your important stuff to CDRom.
Step one: install the XP basics
The challenge is to get the XP-setup to load two drivers from one floppy disk, this requires merging the txtsetp.oem files from both the S-ATA and RAID driver. Save yourself time and use the one I made, listed above. The rest is easy: press F6 at the installation start, setup will ask for the disk and assign the two drivers from the menu. Once XP is up and running (in VESA mode) run windows update.
Step two: install the video driver
The XP driver from the AR21M is supposed to work, but it doesn't run stable on (my) AR31M. Alternatively, download the NVidia unified GeForce Go driver instead, place the new *.inf file in the install directory and run setup from there. Note, check http://www.laptopvideo2go.com to make sure you have the right *.inf file.
Step three: sound
Install the audio-hotfix KB835221 from the AR21M audio-driver directory before installing the actual driver.
Step four: install all remaining XP drivers and utilities from the AR21M, except for Bluetooth and the camera
It may be a bit of a puzzle, but simply go through all unidentified devices in your device manager and 'update driver' with drivers from the AR21M XP driver CD. Skip the UGX driver for now.
Step five: Bluetooth
The 'unknown' UGX driver is a really annoying one. It's not recognized by XP and you can't seem to download it anywhere. I found this excellent instruction on how to trick XP into using its own driver & stack (instead of the Toshiba one) which works just as well:
Go to Device Manager and find the "UGX" with the exclamation point, and "Update Device Driver". Tell it you'll find the software, and when it gives up, tell it to show you all hardware available. Select Bluetooth, and then "Alps USB Bluetooth Adapter". Let it install the drivers. After a restart, your bluetooth adapter should be functioning normally, but with the Windows stack instead of the Toshiba one.
But... if Windows won't let you use its built-in driver, go to Device Manager, select the UGX, and go to Properties. Under the Details tab, select "Hardware IDs" in the dropdown box, and copy both of those "Vid\Usb...." strings. Edit the "bth.inf" file in your %windir\inf directory (probably c:\windows\inf), and add new lines under the Sony section, with a name of your choosing and the PnP IDs you copied above. Just follow the same format as all the other lines in the Hardware section of that file. It should be easy enough to figure out. Save it and try the above again.
Step six: the Camera
In the device manager, XP will probably already have recognized the camera as a USB Video device, and it may actually already work fine. But on my system it didn't, whenever I installed the VCC4 driver (from your AR31M-Vista driver CD), the device would fail to start. I found an instruction somewhere on the web (can't remember where exactly) suggesting this could be because of faulty power handling at USB-hub level. To bypass this, go to you Device Manager, click view-by-connection and the find the USB Hub to which the Video USB device is connected. Open its properties, click the Power Management tab and then uncheck the option allowing windows to switch the device off. This worked for me.
Step seven: the missing memory stick icon
The annoying 'blank' memorystick icon... luckily there are people on the web looking into stuff like this and publishing solutions. It's actually quite simple:
Copy snymsico.dll to your C:\WINDOWS\
Edit registry (run > regedit): HKLM > Software > Microsoft > Windows > CurrentVersion > Explorer > AutoPlayHandlers > DeviceGroups > MemoryStick
Set Icons to %SystemRoot%\snymsico.dll,0
Set NoMediaIcons to %SystemRoot%\snymsico.dll,1
What this does is, gray out the memory stick icon when no media is inserted, then when a memory stick is inserted it changes the icon to blue.
Step eight
Enjoy your awsome AR31M, in a clean, lean and mean XP environment (and forget about Vista).
Costas
Thanks a lot for this guide, it helped me a lot to downgrade to XP my AR31E.
Now my problem is the Audio Driver, Sigmatel CXD9872AKD
It's quite strange. When I install the AR21 series drivers for Audio, everything looks OK. I try to play a mp3 file - it works. But when I close the player and try again, it doesn't work anymore, Winamp says the audio device is not avaible or similar.
Nothing appears wrong in the Device Manager, but I can't play any sound anymore. 😞 
Hi All!
Firstly thanks for the guide costasp! I've been trying to downgrade my AR51M from Vista and stumbled accross your post that pointed me to a few things I didnt know.
For anyone else who is looking to convert an AR51M to XP, most of the AR21M stuff works as does a few of the Vista drivers that were installed onto the laptop when it was shipped. I did however, use the WIFI driver from Intel's website and the ethernet driver from Marvell's website.
I do however have a problem with sound 
I've installed the Microsoft hotfix before installing the sound drivers (as is suggested almost everywhere) and then installed the Realtek and Sigmatel drivers. Everything seems to be OK and there are no errors in Device Manager but there is no sound produced?!?! I checked the Audio settings in Control Panel and it only lists the optical connector as being an output source.
Anyone know what this is and how to fix it? I've tried numerous versions of drivers and even different hotfixes but nothing seems to work.
Also I have installed what seems to be all the Vaio utils but I have got problems with certain buttons (such as eject) and keyboard function keys (such as adjusting screen brightness) Is there a certain piece of software I've missed or a setting? Cant find anything obvious.
Finally as a general question, does anyone know how to enable RAID on this system (or if it even supports RAID?) It seems to have the Intel storage Manager for doing such a thing (although this wont install under XP, yet!) but I cant find anywhere in the BIOS or drivers to enable it.
If anyone wants any info on what I did to get XP onto my AR51M, let me know!
Steve
(Happy Vaio Owner + Vista Downgrader) :smileygrin:
Finally I found a driver for my audio, I'll upload it tomorrow so you can test it, Baccynet 
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