You could add the AHCI drivers to windows.
There are many links to doing this and the proper registry entries that must be modified.
Just google it, even MS has an article about it.
Yup, I already am running windows XP in AHCI mode with hacked drivers and is working fine. Ubuntu is running in AHCI mode as well. Leopard, on the other hand, works on AHCI mode except it only sees 2 SATA devices (port 0-1) .. ports 2-3 doesn't work (GA-P35-DS3L) and i have 4 sata devices.
I have to go to the BIOS everytime just to change AHCI to IDE so that "Leopard" can show 4 sata devices. When i'm done with Leopard and decided to go to Windows XP, I then restart, go to the BIOS (again) change back IDE to AHCI so I can successfully boot to XP. Then when I'm done in XP and let say, i forgot to do something in Leopard, reboot from XP, go back to BIOS, blablalba...
Regarding faster in AHCI mode debate, yes, there are no difference at ALL. They are identical. However, I need to use hot swap of sata devices in XP. This only works when AHCI is enabled (afaik). Also, all my 3 OSes boots way way faster when AHCI is enabled. In my case, its weird that my Leopard is slower in IDE mode .. I really don't know why ... like opening applications .. running multiple apps at a time .. alot of freeze times .. but the funny this is when I run benchies in this same PC for both AHCI and IDE .. its the same!
*BTW, I was using the old VIAATA*
I think the newer hacked drivers that Dune made, fixed my slow Leopard in IDE mode. I don't experience my Leopard slowing down anymore after applying the new kext.
Thanks to Dune!
Anyway, I was just hoping that all my 4 SATA ports will work in AHCI mode. I guess I still have to wait for that magical kext.