The four hundred on both of those processors is referring to the Front Speed Bus of the processor - totally different thing. I believe if that Celeron is a 2GHz then it would have to be based off of the Pentium 4 chip. If memory serves, the P3 only went up to about 1.5 or a little higher, I don't remember it making it to 2GHz, but I might be wrong. In any case it's more that likely that the Celeron is going to be rated at a higher speed (GHz) than the P3. However, the Celerons are a lower grade version of Intel's chips, the reason why a Celeron and a Pentium would be rated the same, but perform differently. To make a long story short, the Pentium will be a higher grade, but probably older, the Celeron will probably be faster, and newer, so if it looks compatible, I'd take the Celeron.