I have an Athlon X2 4400+ and the one way to overclock is to adjust the FSB in your BIOS because the multiplier is locked. It is set stock at 200mhz, try bumping it up little by little until you get an error or crash. Then adjust the voltage til you no longer have problems. Also you will need to downspeed your RAM to 333mhz. It is currently set at 200mhz (DDR RAM PC3200 is 2x200mhz = 400mhz) so you want to take it down to 166mhz. You need to make sure you have a good CPU cooler, your stock cooler is not going to cut it. So make this your first priority. There are extensive overclocking guides on this forum you can use for reference.