Head to the Asus support website here:
http://support.asus.com/download/do...SLanguage=en-us
Choose motherboard, socket 939, A8V and click search, then you should get presented with a series of tabs.
Click the "Drivers" one and choose the package with a description of:
"VIA VT6420 (VT8237) SATA RAID Driver Package Version 2.20D WHQL."
for Windows 98SE/ME/NT/2K/XP/2003.
The main folder will be called VIARAID, go in there and then choose "DriverDisk", in there will be an exe called MakeDisk.exe, place a floppy disk in your drive and run that, then you'll be sorted for the F6 driver select screen when installing Windows. There is also a readme in the main directory that will tell you exactly which files to copy over if you'd rather do it manually but the MakeDisk executable should work fine