Which Celeron's and which Pentium's? Because it matters here.
Pentium 4's can be single core, Dual core or single with HT.
The newer Pentium's (after the P4's) are all Dual Core, while at least one of the newer Celeron's is only single core.
In any case, the Core 2 Duo's are not Pentium's or Celeron's. Completely different thing altogether.
Edit: Damn, spent too much time getting to this one, lol.