I have got two CPUs and Motherboards,
One is Pentium 4 2.4Ghz and Motherboard is Gigabyte with Intel 845D chipsets, this one is the older one
The Second one is Celeron D 3.0Ghz and Motherboard is gigabyte with VIAP4M800 Chipsets

The first one is one with the pins and the celeron is the new type i.e LGA775 package so i cannot interchange the motherboards because the older motherboard only supports Pin-type CPU.

I have a Nvidia Geforce 6600 gt graphics card, 1GB DDR ram and 250Gb hard disk. I mean with every component same i get difference performance on changing the motherboard and CPU.

The problem is that the performance especially of the games is too low on the new celeron D 3.0 ghz, i mean the games which barely reach 20 frames on the Celeron D processor and VIA chipset mobo, run at nearly 50 frames on the older CPU and mobo(P4 2.4 ghz and intel chipset mobo). I cant figure out where the problem lies, is it the chipsets or the motherboard or the cpu. I had made up my mind to buy a new P4 processor but someone told me that chipsets could be the problem, so i got more confused.

So please tell me where the exact fault lies, by the way I cannot use the old P4 cpu and motherboard because with it the computer crashes everytime, that is why i bought a new cpu and mobo. What should i do? buy a new mobo with good chipsets or a new cpu? Please help me with this. Please specify some names too.

Your problem lies with the Celeron D at 3.0GHz. A Pentium 4 at 2.4 GHz is a lot faster than a Celeron @ 3 GHz. I reccomend you sell you Celeron cpu and buy a P4 at 3 GHz

The Celeron line (whether it is a Celeron D or not) cannot compete at all with Intel's mainstream Pentium line. Any Pentium 4 (barrring the older Williamettes maybe) can crush any Celeron out there quite easily.