No, DDR 400 will not work. The best thing you can do is call Dell and give them your information. Model number and that kind of information and let them tell you what kind of ram you need. If you put the wrong type of ram in your machine it could cause major damage. There are so many different kinds of memory out there, not to mention high and low denisity. Your machine may use PC2700 high density and if you try to use PC2700 low density it will not work. One other thing that you can try is uninstall a stick of your ram and write down everything on the stickers and then go to some place like kingston memory and use their memory locator to find what you need.