Use cpuid to identify the motherboard chipset. It will determine whether a cpu upgrade may work. You might have better luck posting this in one of the dell forums.
A few have used the 125W AM2 Athlon 64 X2 3.0 GHz $80. You'll need to follow the cooling advice you'll find in the Dell support forums for the hotter 125W CPUs.
Hi thanks for all your replys its much appreciated. The chipset i have is a nforce 410/430 mcp according to cpuid. Does this help in identifiing the cpu i could upgrade to? Thanks again