Haha, go for the Abit BX6 REV 2.0......it's the best. I still am using it. After buying it and overclocking the Celeron 300a to 450, I am using it to overclock at Celeron 566 to 850mhz.
To overclock, just pop in the cpu and when it boots, go to the bios menu. Then, just change the BUS speed from the default 66mhz to 100mhz.
300mhz = 66mhz X 4.5
450mhz = 100mhz X 4.5
You can't do anything about the 4.5 cuz it's the built in multiplier that is in the chip.