gfd is a gold finger device. This unlocks the athlon so you can change the multiplier. For example, since you have a 750mhz you're multiplier is 7.5 and the front side bus is 100.
7.5 x 100 = 750(actually since the bus on the athlon is ddr its 3.75 x 200 but you won't see that in any of the gold finger descriptions)
With a gfd you can overclock your athlon by changing the multiplier anywhere from 3.5-10.5 (350-1050). One drawback is that you have to take the plastic case off your athlon and plug it on a row of pins near the processor. There is a chance of damaging the processor while opening the case. check out http://www.k7oc.com
for more information.