Although the CPU will eventually limit the FSB, I've found that the chipset and peripherals are more likely to cause a problem first.
There is a well-documented problem with all of the first generation motherboards that used the VIA KT133 chipset. These chipsets were released before the availability of the 266 FSB CPU's from AMD. The early KT133 chipsets are usually limited to a FSB in the 107 / 110MHz range. With the release of the 266MHz ("C") CPU'S from AMD, VIA addressed this problem with the introduction of the KT133A chipset with "official" support for FSB's of 133MHz and above, some have reached 150MHz and beyond with this chipset. Most people get to the 140MHz range before running into problems with the peripherals such as the video card and NIC in particular.
Personally, I've run a couple of DURONS at 140MHz on both an ASUS A7V133 (KT133A chipset) and a FIC AD11 (AMD 761 chipset). Many others have achieved similar or better results.
If you are using a chipset that does support FSB’s in excess of 133MHz and are still having problems reaching this bus speed I would recommend that you start looking at the support hardware such as the above-mentioned video card, NIC etc. You may also want to verify that your memory is capable of the higher bus speed as well, most motherboards will let you lower the memory bus speed and timings independently of the FSB.
Another potential problem area is the power supply, although a good 250W psu will usually suffice, most people have better results with higher wattage and better quality (more expensive) units.
I hope this helps.
Good Luck!
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