well, xp2100+'s run on air cooling, so if you overclock the 1800, it's not like you're gonna have to go for a water cooling set. but if you only have the amd factory heatsink, you might not want to overclock until you get a better hsf. as for performance increase, it depends on what kinda software you run and if it'll max out your cpu. if you just do word processing, web surfing, and another low cpu utilization programs, then you don't need to overclock. if you're a serious gamer, or into distributing computing stuff, you want the most out of your cpu and want to oc that baby. the xp's scale pretty decently, so overclocking is a good option.