Not familiar with the BIOS in that board; post some of the advanced chipset settings for me to look at and I can tell you what to set.
I know on the first dual AMD tyan boards there were minimal options none of which would make much difference.
edit
onna side note I noticed you said 1800+ XP's
you could have some issues with these CPU's particularly when it comes time for them to make use of their L2 cache. MP's were designed with multiple CPU configurations in mind; and have a few extra instructions to intelligently handle cache coherency. Jakes a bit on the correct side; asside from some lower performance than a pair of MP's; you might see some stability issues depending on quality of the motherboard and wether you have ECC RAM.
On another side note; one BIOS setting that comes to mind is to disable video BIOS shadowing as well as system BIOS shadowing. Neither option are required and can cause slower video performance; and occasionally unstable performance.