Ok well your FSB is probably 133, so the easiest way is to just bump that up to 160. You'll then have to make sure you set the RAM to the right voltage and timings and also by boosting the FSB it will OC the CPU a bit, so you'll also have to make sure that everything is good in that regards as well. I'm not sure how much leeway you have in the FSB:RAM ratio, I'm assuming it tops at 1:10 but if it goes higher you can set a lower FSB.
The other thing is, let's say your ram is rated 1600mhz CL8 (CL8 is the timings, ie: 8-8-8-24). You can run it at 1333mhz CL6 or CL7 (I know 1400mhz CL7 would work, so you might shave another notch off the timings at 1333mhz) to do this just make sure to run the ram at it's proper voltage (usually 1.65V) and then you won't need to OC the CPU at all.