However am I right in thinking that the CPU clock speed is 100 MHz up to about XP1700+ or 1800+ and 133 MHz above that? I thought it strange that it wouldn't even power up when I'd got it set for 133MHz and it wasn't until I rejumpered it for 100 MHz that it worked at all.
No definately wrong!!!
According to the gigabyte website if you have a GA-7VAXP (is yours a typo as you say GA7AVXP) if you have a AMD AthlonXP 2100+ (Palamino) then the FSB should be
266 @ a ratio of 13 if you have a Thoroughbread it is set the same.
Definately not FSB of 100 or 133.
Have a look here
AMD K7 Series MOB Socket A CPU
Hope that helps, if it is the wrong MOB sorry, but that was the only one I could find.