I just did a W2K install on a Iwill KK266R this weekend (raid turned off via jumper so it is the same as KK266). I actually did many many installs as I played around with several versions of drivers and here is what worked the absolute best for me:
Used the bios that comes with the board (march 5).
Partition and Format Hard in FAT32 and install W2K.
Install the via 4 in 1 drivers version 30.
Get them here (zip file, so I used WinZip):
4 in 1 v 30
Install the Iwill recommended via 4 in 1 drivers version 23 from Iwill website. Get them here:
4 in 1 v 23
Install audio drivers from cd that accompanies board.
Drivers for whatever else you got.....
The reason for the two layers of VIA drivers is that the IDE driver for version 30 works great with W2K, but the other three drivers in version 30 don't work as well with the iwill board as the version 23 drivers. I think this is why on iwill's support sight they say "please use version 23 drivers". The 4 in 1 version 23 from the iwill website is really 3 in 1 since it doesn't have the IDE driver (hence your version 30 IDE driver will stay on there when you install the version 23 from iwill). If you install the IDE driver that comes with the power installer cd then it will do crazy stuff like say your IDE drives are SCSI drives. I really got great benchmarks on the system, memory, and hard drives with the above installation method. The only thing I used from the cd was the audio drivers.