I need to know what's the highest speed my mobo will take for RAM because I want to upgrade. I have DDR2 400 256MBx2 in there now but NewEgg only has one option for DDR2 400. I would have plenty of options if I went to a higher speed like 533 or whatever. I know I shouldn't mix and match the RAM speeds so I was going to get 2GB and then just get rid of the old 512MB sinc they would be different speeds.
It's a Dell Dimension 4700. I tried Google but couldn't find anything.

Nevermind, I suck at Google.

Okay, now I do have a question. Last night I bought 1GBx2 of DDR2 533 RAM and in my computer I have 256MBx2 of DDR2 400 RAM. I can leave the old 400 RAM in but that will make the new RAM run at the slower speed, correct? Would I be better off just putting in the two new gigs of 533 (I believe that's the highest speed my mobo supports) and ditching the old 512MB?

use the new DDR2533 ram and ditch the old one.