Upgrading RAM in a Dell Dimension Dim 3000

Hey new buddy, CoolDr. I see you are the computer guy, so I thought I would direct this one to ya. I have a Dell Dimension Dim 3000 with an Intel Celeron 2.4ghz cpu. I tried to upgrade my RAM from 512mb to 2gb (2 x 1gb sticks). I purchased them and they were the same specs except that the 512 in the computer said pc3200u and the ones I purchased sadi pc3200. The new sticks and the old stick all are 400mhz 184pin DDR. The only difference is that the old one has the "u" at the end of it. Does that make a difference, I have seen them listed on eBay in the same listing as pc3200 and pc3200u, so I thought they were the same.

Now the problem. When I install them, the warning buzzer sounds, like it does if the RAM is not fully seated. I have tried the 1gb sticks together and individually in each of the two slots, and same results everytime. I put the origional 512mb stick back in, and it works good (I'm using the computer now).

Anyhelp would be greatly appreciated. I bought the sticks off eBay and hate to be out money if the guy didn't have them listed right and they should have worked.

Dean