Well, no, you can't just buy any processor and have it work in any motherboard. You have to find out what processors will work in the motherboard you have and buy one to suit it.
The first step is to identify the system board and locate a specification to determine what processors are compatible. Brandname manufacturers like Dell, HP etc publish their own specifications - if the system is generic, it will depend on the mainboard manufacturer. The brand and model is usually stenciled on the board, may be displayed at boot or in the BIOS setup screens, or can be found using a diagnostic utility like Everest Home:http://majorgeeks.com/download.php?det=4181
(This is an old version that may not understand all recent hardware, but will still report brand & model strings.)
Edited by Platypus, 03 July 2009 - 07:28 AM.