Seems like your pushing the limits, as the FSB involves a lot of parts. It's always best to find an optimal setting between the FSB and multiplier. In your case you can only change the FSB, which is annoying. I know what I'm talking about, my CPU is also multiplier locked.
There are usually methods on how to disable the multiplier lock but they involve modding of the CPU itself or the motherboard.
EDIT:
Your mobo supports a maximum memory clock of 166.5MHz(=DDR333). Basically you could consider the max stable FSB to be 166.5MHz, if the mobo has a 1:1 FSB : DRAM ratio. obviously you would need a lower multiplier in order to get a stable CPU OC, but it isn't quite that simple as the AGP slot is also modified by the changed FSB.