Enabling Write cache on disks with RegEdit

Hi,

I am running a 2003 server and the performance is pour,
my system:

Mainboard= AsusP5B-MX
Inte core duo 3.0 Ghz
2048 Mb ram ddr2
3x 320 Gb sata II (300mb/s)
Intel extreme graphics 256 mb
-------------------------------------

When i go in to the device manager the option for the system disk (the disk with the OS) i can set "enable write caching on disk" with the warning that it can be dangerous ... bla bla i know!
After a reboot the system turns it off automaticly, i set it again...and so on every re-boot.

I am looking for the registry key which controls this function , set it and make it read only for everyone, so the system cannot change it for himself.
Nobody seems to know which key this is...or what to set...

is there somebody out there who can help me to kep it set to "ON"
or has a better idea, maybe a BIOS setting that needs to be changed?

thanks