Will a system with a P965 chipset and 667MHz DDR2 SDRAM be able to operate at a FSB speed of 800MHz with a T7250 (2.00GHz, 800MHz FSB, 2MB L2 Cache)?

Yes. The FSB800 of the cpu is quad pumped. (200x4). Memory by default is double (200x2).
 
DDR2667 will run with a 1:1 to ratio with a cpu running at 1333FSB(333x4).
 

What he said.  but to reiterate.
For Intel :  
CPU bus speed Divided by 4 | DDR2 memory bus divided by 2
So your answer is  CPU 200 | Memory 333.
 
Long as the memory is at or above the cpu speed, you'll be set.
 
Thats not to say your motherboard will like the processor, but with that chipset it likely will work.

Isn't a T7250 a laptop chip? And if so all the laptop chips from Intel I know of run on the 478 socket. And a P965 is a LGA775 chipset. How you will get it to work I have no idea but good luck.

^ Thats what I thought so too. Its socket 479 btw, and not 478 or 775.

Opps I didnt even bother to read what cpu the op was intending to use. I just assumed it was a e4*00 or e2*00 series.

 
Hmmm... according to Wiki and what I can find its a Socket P CPU and thats 478 same with Socket M. They just aren't compatable.
 
http://en.wikipedia.org/wiki/Socket_p

There is a P965 that is a laptop chipset.

 
The mobile version is PM965. P965 is the desktop variant PM965 is mobile. Saying P965 would normally indicate desktop. So maybe he just messed up.
 
http://www.intel.com/products/lapt [...] ody+nb_all

Yes this is for a laptop, I suppose I meant PM965.  Sorry for the confusion.

 
Thats fine. Its just that we all know P965 as desktop. Anywho, that chipset has support for a 800MHz FSB chip but you might want to look at this:
 
http://compare.intel.com/pcc/showc [...] ture=en-US
 
This shows all the chips that chipset will support so you might not be able to run that chip you want.

Are you wanting to switch out a cpu on a laptop? Or switch out/add the ram modules?. I hope its the latter. Taking the general hardware knowledge info from this post about the fsb speeds and all, I dont think its a good idea for you to try and change cpus in a laptop.