I recently got a Tyan Tomcat 1000S (S3950) motherboard and went in circles trying to get the proper drivers for SBS to see the RAID controller.  After consulting with Tyan and doing some searching, I found the drivers.  The Tyan uses the Broadcom ServerWorks HT1000 disk controller, and Broadcom has spun off its storage division (including that chipset) to Ciprico.  (I'd never heard of them;  at first thought, weren't they selling anti-anthrax drugs? Oh, that's Cipro!)

Here's the link to the drivers:  Ciprico RaidCore downloads page.