ok, lets put this shyte straight...
Core2 duo vs Pentium dual core-
Nothing really, Intel just released the e5200 and called it a Pentium dual core to show that it's not the fastest, but also not the slowest... Marketing jargon... They reserved the core 2 duo for the E6xxx-E8xxx. They all use the same architecture, basically anything with an "E" (eg E8400) is a dual core, that uses the core2duo architecture. However why they call the E5200 a Pentium is the cache size and FSB.
So, to the new celerons, basically, they use core2duo architecture, HOWEVER, they have small caches and run on the older 800mhz FSB. The celerons are further retarded but limiting their clock speeds to a maximum of 2.4ghz.
Now in essence, by dropping the core's cache to 512kb (on the dual core and single core), the processor has to use the FSB to gather the information, however, since it's at 800mhz, that is also retarded, thus the processor is pretty bad at applications that use cache (which is a lot of things, but for word processing, general usage, interwebz, music etc it's fine, as soon as you try game, video edit, video encode etc it sucks).
So to sum it up anything with Q=quad core (for intel) anything with E=dual core (for intel, no matter if it's a celeron or pentium, this "E" shows the progression of processors as previously we had Pentium "D" which was single core).
What makes the celeron slow is the cache size, which isn't a train smash if you just want a laptop to do things like web browsing, music, movies(you not gonna have the movie jutter etc) and so on. But if you wanna play games, use photoshop, video encode etc then avoid the celeron...
Honestly, a laptop should be used as a portable device where you do your work on, buy shyte for the web, do general stuff on it while away from the desktop... you shouldn't be aiming to video edit etc.
Edit,
How much do you have to spend on the laptop? I mean, we all could help you
