Refresh my memory for me, what is the default vCore for an Athlon X2?
The last AMD OCing experience I have is my Opteron 170 which is sitting outside in the garage waiting for my nephew to make all A's on his report card.
Are you using the stock heatsink and fan?
Some tips:
A) Keep your HTT (HyperTransporT) speeds under 1000. I've seen some boards handle up to 1200 but there is little to no benefit to keeping it that fast. When you start to overclock from 200Mhz turn the HTT down to 4X.
B) You can usually get a few more MHz out of the CPU by changing the Command Rate on your RAM from 1T to 2T.
C) If you are using the default HSF do not supply more than 0.2V over stock to the CPU. People who are running high vCore's either have good aftermarket cooling or they don't care about destroying the CPU.
D) Keep your RAM as close to stock speeds as you can (i.e. run a divider in the BIOS).
E) Ditch the OS program and poke around in the BIOS, you'll learn more that way too.
This isn't AMD specific but it should help you get pointed in the right direction.
http://www.pcstats.com/articleview.cfm?articleID=1804