Okay get this combo-
For the CPU this mobile 2400 athlon XP is a very good chip- http://www.newegg.com/app/ViewProduc...103-439&depa=0
It can easily overclock to 2.4ghz, which is fast for an amd. And since it's mobile it uses less power which in turn means less heat.
For the Mobo get the Abit NF7-S as earlier suggested- http://www.newegg.com/app/viewProduc...127-166&depa=0
It has everything you will need to overclock this baby to it's full potential.
And since the cpu is OEM (meaning it doesn't come with accessories) you will need a heatsink and a fan, this one will do you real good- http://www.newegg.com/app/ViewProduc...106-037&depa=0
And if you order that tonight it's on sale.