My asus p5k deluxe motherboard and e6600 processor are reported as not having hardware DEP (Data Execution Prevention) in Vista's DEP setup panel. I need to test the software I write with a machine with hardware DEP, so I guess I need a newer system. Can I just get a newer 775 socket processor, or will a new motherboard be required as well?
This is a bug in Vista then. All modern Intel and AMD x86 processors support the NX/DX bit. Oddly, I've never heard of XP or Vista not able to detect this properly. You can check your bios settings to see if there is a way to disable it from there. I know Virtualization can be turned on or off from a bios setting in most motherboards. I've never seen DEP settings in the bios but anythings possible.
I was browsing the Manufacturer's faq. You probably need a bios update to enable DEP. The processor does have it built in but the Motherboard has to take advantage of it.
You may or may not have to reinstall Windows for it to detect it properly. In any case I'd back up critical data before doing a bios update. You shouldn't have any trouble but if something goes wrong during a bios update it can turn your system into a boat anchor.