I finally decided to ditch my old Core 2 Duo 6400 Processor (~2.13 Ghz) and upgrade to a quad core. My issue is that my machine is about 4 or 5 years old now. My mobo is the Intel DP965LT and the my current cooling for my processor is the Freezer 7 Pro.

I purchased the Intel® Core™2 Extreme Processor QX6700 (Quad Core), I know I will need to update BIOS for the new CPU, but I believe that is worth it. While waiting for the new CPUs arrival I've been researching if my current cooling system will be enough. The Freezer 7 Pro is a small fan with a small heat sink (98mm I believe). All the aftermarket fans I've been looking at are 120mm and up. Will these be too big to fit in the holes already there for the push-in style heat sink & and fan slot already in my cpu?
I need to find a heat sink and fan that will fit in the slot where my Freezer 7 Pro has been. I really appreciate your help and suggestions.

p.s. My new CPU won't be coming with heat sink or fan, since I bought 2nd hand CPU. Also, I don't plan on overclocking....the 2.66Ghz out of a Quad core will already feel like a ferarri compared to my old 2.13 Dual

Current System Specs:

Operating System: Windows XP Home, SP3
Mother Board: Intel Model #DP965LT; Chipset: Intel P965/G965
Processor: Intel Core 2 Duo E6400 ~2.13Ghz (this must go!)
Memory: 3 GB DDR2 RAM
Video Card: NVidea GeForce 9500 GT w/1 GB Memory

As long as the heatsink is made for a socket 775 CPU it will fit the mounting holes. IMO, if you are not planning to overclock, the Arctic Cooling Freezer 7 Pro is enough. If you decide to get a larger heatsink/fan anyway, most that are designed for a socket 775 should fit. Just make sure the larger heatsink/fan won't interfere with other components like side case fans or extra tall heatsinked RAM.

If this PC is for gaming, consider replacing the 9500GT.

Oh ok! I guess I will stick with the Freezer until I decide to over clock.
My hesitation on replacing the 9500GT is that it has 1MB of memory and that's kinda a lot I'm thinking. What would be a reasonable replacement for it? One that wouldn't cost more than say $150. Thanks!

Sapphire HD 4850 Vapor-X 1Gb ($97 inc shipping) no DX11 though but a lot of performance for the price.
MSI GTS 250 1Gb TwinFrozr ($100 inc shipping) for it's nvidia equivalent.
Asus HD 4870 1Gb ($122 inc shipping) higher performance. excellent gaming at 1680x1050
Of the newer DX11 capable cards...
PowerColor HD 5770 512Mb ($135 inc shipping) would be reasonable step up in performance from the HD 4850/GTS 250. And a 1Gb version here for $140 Both these cards (and the HD 4870) will allow pretty good all round gaming up to 1920x1080 resolution.

I was going to suggest a Radeon HD 5770 but dividebyzero beat me to to it and included it in his suggestions. I prefer one with a dual back panel bracket because it provides a ventilation path out the back. The Powercolor HD 5770 512MB, for example, still takes up two expansion slots but only has one bracket and no exhaust outlet to the outside. It's nothing against the Powercolor brand as I have a Powercolor HD 4890 and HD 5870 myself.

Oh my I feel nastalgic, I remember when I got my qx6700 a few years ago, overclocking to 3.5ghz. Although I was using a coolit 300usd cooler that workeed ok at the time. This brings me back. Everything you have seems okay. I dont know about the 4850, maybe a slight upgrade would do you well in the vga department.

Hmm 5780? Is there something which we don't know about at TS?

Well typos apart, I believe 5770 would be bit better choice over the rest, because of its reasonably good performance and DX11 support.

Ya got me. Typo is fixed. Thanks.