Neoseeker have an interesting guide about asynchronous bus when it comes to overclocking. If you've never heard of asynchronous bus, I suggest you check this out.
Currently the most popular chipset for a single CPU Athlon system is the KT333. It supports things like ATA 133 and DDR333 that have quickly become standards. Most KT333 board manufacturers have opted to use an asynchronous bus to support DDR333 instead of adding in a 1/5 divider and supporting a true 166Mhz bus. I'm not a big fan of this at all. The gains of running an asynchronous bus aren't as big as you'd expect.More information at Neoseeker