"Microsoft Windows XP Service Pack 2 (SP2) helps protect your computer against the insertion of malicious code into areas of computer memory reserved for non-executable code by implementing a set of hardware and software-enforced technologies called Data Execution Prevention (DEP). Hardware-enforced DEP is a feature of certain processors that prevents the execution of code in memory regions that are marked as data storage. This feature is also known as No-Execute and Execution Protection. Windows XP SP2 also includes software-enforced DEP that is designed to reduce exploits of exception handling mechanisms in Windows."
For more information about Windows XP SP2 memory protection and how to configure it, check out this link to the full article:
Thomas W Shinder, M.D., MCSE
Sr. Consultant / Technical Writer