The chipset used in the Dimension 2400 will handle 2 GB per Intel, who makes the chipset. I can't be absolutely certain that the computer will handle 2 GB as I've never put this much in it, but one of my 2400's has been working happily with 1.5 GB for about eight months now. I used Kingston memory, but I'm certain that there are other vendors, such as Crucial, who supply memory that is compatible with the Dimension 2400.
You're right Jack. I borrowed two 1gb sticks and put them in the 2400 and it recognized both of them.