I have an old Dell Dimension 9150 with a Pentium D 940 dual-core CPU that I would like to upgrade (Intel 945P chipset).
 
What are my upgrade options? I can use any Intel 775 chip that will fit?
My ideal solution would be use the Intel Core2-Quad Q6600 CPU from my main PC and buy a new CPU for that PC. This way both my machines get more grunt. Would the Q6600 CPU work in the old Dell?
 
FYI, the CPU needs upgrading as the Dell PC is being used to run CPU intensive webcam monitoring software (Vitamin D). 
The disk & memory performance is fine it's just the current CPU that is often running at 100%.
The other existing specs are: 2GB Dual channel 533MHz RAM, 2 x 250GB SATA HDD, nVidia 8600GT graphics card.