Is there a significant difference between using Celeron and P3?

I think one of the reasons is that the celerons have a smaller cache then do pentiums, cutting down the cost. THis is something to search on google, should be very easy to get a answer

yeah, there is, especially if you are running php/mysql. try to search anandtech.com, they have benchmarked some different server a few months ago (AMD XP/MP, Intel Xeon and P3).