No, the FSB is not the only part of how fast a CPU can perform calculations.
The FSB determines how fast the CPU can get data from memory, but the clock speed of the CPU determines how fast it can deal with that information once it has gotten it.
In this case I would probably expect the Pentium 4 to be faster, but it depends on many other factors. There have been many generation of Intel products that have borne the Celeron (aka "cheap") brand name.
Comparing FSB speed is only really useful if you are comparing two near-identical processors that have the same clock speed but different FSB speeds