Sorry bud, but you can't do that. The Core Duo needs an Intel 945 or better chipset. I bet your Celeron runs on the venerable 855GME chipset, which will not be able to feed a Core Duo's 667MHz FSB from DDR2-667 RAM. It has a 400MHz FSB limit and can handle DDR333 at best.
However, you could put a Pentium M Dothan 7x0 series chip in the Dell's board and it would be much faster than that Celeron. 2.1GHz is the fastest 400FSB Pentium M made, and that should fit your laptop perfectly.