I just upgraded a Windows 2000 Server by installing a dual Opteron using the Tyan 2885 with 8 GB RAM. Everything appears to be working, but Windows seems to think it is using a single processor with 4 GB RAM. BIOS settings reflect the dual processors and all 8 GB.
Device manager shows a Standard PC. I am running Service Pack 4. I installed the AMD drivers from the Tyan CD.
Was it installed as a single cpu then you added the second CPU, or was it built form scratch as an SMP system?, if you upgraded from a single cpu you might have to re install inorder to use the SMP HAL/kernel or maybe just update the computer HAL in control panel /system.
If the above is the case wait for a bit more expert advice on upgrading the HAL as its somthing I am not very clued up on and if done wrong you will have to do full reinstall.
PS I am assuming that win2k server has support for dual cpu's without and additional licenses from M$