The Barton 2500 is a great CPU. If you are fortunate enough to get your hands on an "unlocked" one, one that was put out before week 39 I think...You can Easily overclock that bad boy like I have mine to 3000 and even 3200 speeds! As far as motherboard, get an Nforce2 chipset motherboard. They are great for athlon XP CPU's. Somewhat faster than VIA's from what I have experienced. A good board would be the Asus A7N8X or an EPOX 8RDA+ like I have
Good luck.