ive got amd athlon 2000 too i think it was originally 1.67ghz??

anyway mine is now 1.8ghz and has been since last august and its fine

make sure you got a decent amount of fans/ventilation and also a good amount/make of memory..memory is a big key to how much you can overclock it

and its been said before but ill say it again

OVERCLOCK AT YOUR OWN RISK
ALL PC'S ARE DIFFERENT SO ALL HAVE DIFFERENT LIMITS
JUST BECAUSE I CAN OVERCLOCK MINE TO 1.8GHZ DOES NOT MEAN YOU CAN

YOU COULD MAYBE OVERCLOCK IT TO 2GHZ
YOU COULD MAYBE CLOCK IT TO 1.7GHZ

increase it a tiny bit at a time and when your pc starts locking up or freezing then stop and reset BIOS using the button on your motherboard and set it to a couple of digits below the number you started getting problems at

and also i suggest monitoring your tempreture as you really dont want to fry your CPU

athlons already run at high tempreture at default clock speed