Just found this
Will a AthlonXP run in a A7V / A7V133 /A7V266 etc. that does not officially support it?
The AthlonXP might work on non-AthlonXP compatible A7V series Mainboards, too - even on the old A7V KT133. The newer A7V BIOSes, for example, include code to support the AthlonXP and Duron 1Ghz and up. But noone will guarantee that it will work - so don't count on it. You might get almost any AthlonXP to boot, but that does not mean it will run stably and reliably. I read that AMD told people that the AthlonXP will only run reliably with 133Mhz FSB - so unlocking it and running at 100Mhz FSB with higher multiplier might get you into trouble.
In my opinion this compatibility or incompatibility comes from the fact that between Athlon and AthlonXP the specification for the processor bus has been changed. As far as I know for AthlonXP so called "L-C-L" Filters are needed, which are NOT implemented on older mainboards. Without these filters it depends on how the production tolerances of CPU, Chipset, Mainboard etc. affect each other. Either it does simply not boot, it works unstably, or it works perfectly. Noone can tell you if your combination will work - even if others have had success with a certain combination, it might or might not work for you. So only try using AthlonXPs on mainboards that are 100% fit for the purpose (see tables and links below). If you want to try on a not officially compatible board, than be prepared to run into trouble.
Especially on the A7V the biggest drawback is it's low FSB of 100Mhz, while AthlonXPs are designed fior 133Mhz. So the resulting speed at a given multiplier is lower than it should be. Overclocking the FSB is a very bad idea in my opinion, because on one hand the A7V doesn't overclock well, on the other hand FSB overclocking overclocks everything - from RAM to IDE. Only do so if you regard the data on your PC as expendable.
Heres the link to the full post