Gavin:
I have the same Promise controller, mine is on an Asus P4P800 E deluxe, I have used it in BOTH RAID & ATA modes. Whichever you use, you install the drivers from within Windows, through Device manager, in the zipped file you downloaded from Asus, there is a text doc with instructions on how to do it, here are the instructions from text doc:
1. Please check BIOS setting was RAID mode or IDE mode (default was RAID mode).
2. Right click "My Computer" icon on the desktop. Select "Properties" when the menu
appears.
Or you can
Press "Start" button. Move highlight bar to "Settings" and select
"Control Panel". Double click on "System" icon.
3. Select "Hardware" page and then click [Device Manager] button.
4. View devices by type and find "RAID controllers" node.
5. Right Click the "RAID Controller" node.
6. When the menu appears, click the "Properties" item.
7. Please select [Driver] page to update driver.
8. Select "Install from a list or specific location[Advanced]" and then press next.
9. Choose "Don't search.I will choose the driver to install." and then press next.
10. Select "Have Disk". Browse the RAID mode path {CD-ROM Drive}:\Drivers\Promise
\378RAID\WinXP or IDE mode path {CD-ROM Drive}:\Drivers\Promise\378ATA\WinXP to
the driver and click OK.
11. Press Next.
12. Press "Continue Anyway".
13. Finally, press Finish to complete the installation.
14. Please restart you computer for these changes to take effect.
Hope that helps you.