How large of a difference would I see between a Celeron 3.46GHz processor and an Intel Core 2 Duo 1.8ghz?

there will be a huge diffrence. the intel core 2 du is much better then the celeron. the c2d is 2 cpus (cores) on a single socket. it has a larger cache (4mb) and it will be much faster even though thats not what you would think if you were going by the clock speed.