I have a Revision 4 of the Tyan Trinity 400 board, and it does support rudimentary overclocking. Go to the "Chipset Features Setup" page in the BIOS and you'll see an option called "CPU Clock/Spread Spectrum", which allows you to change the FSB speed. There aern't too many bus speed options, but it does work. Right now I have my Celeron 466(7x66)Mhz running at 525(7x75)MHz.
Anyway, you have to careful because you cannot change the AGP/PCI dividers from the default value for the CPU. So a 66Mhz CPU will have a FSB:AGP clock ratio of 1:1 and a FSBCI ratio of 1:1/2, even if you use a 100 MHz bus speed. This is also true if you use a 100 MHz CPU, which has a FSB:AGP ratio of 1:2/3 and FSBCI ratio of 1:1/3, or a 133 MHz CPU, which has a FSB:AGP ration of 1:1/2 and FSBCI ratio od 1:1/4.
Hope this helps you.