Memory speed is linked to the FSB speed via the memory divider. If the divider is set to 1:1, or 400, then the memory will run at the same speed as the FSB. Set it to 4:5, memory speed will be a fraction of the FSB (4/5); set it to 333, and the fraction will be 333/400.
Look for a page in your BIOS called DRAM settings or something like that. An area devoted just for memory timings and settings. Motherboard reviews look at the BIOS in detail, so look for a review of your mobo to find where the memory timings are.