Yes. My old stick works fine in windows xp. I was having troubles installing xp. It would hang up in certain points during the installation. After remembering that a technical support guy from ms had mentioned something about somebody having some "fancy ram" that was causing them trouble, I decided to try my SDRAM just for the install. It worked fine with the sd. Windows xp installed and it started up. Then I figured I'd switch back to my ddr ram because I thought it was only causing problems during setup, but windows xp won't even start with the ddr ram in. However, windows98 (when it was installed) started fine with the ddr.