The TDP is the 'recommended' maximum power the Cpu should run at. If that figure is exceeded, either because the Cpu itself has a higher TDP rating or it's overclocked, it can cause overheating of the Cpu and/or of the VRMs (Voltage Regulator Modules) which supply power to the Cpu.
In your question that 965 TDP 125 Watt Cpu would work but if it runs near 100% for long enough (a few minutes) it could get hot enough to throttle back to a slower speed or even shut down the PC. Plus it could overheat the VRMs which would damage the motherboard.
Basically you need a motherboard that can supply enough power to the Cpu and Cpu cooling that can keep the Cpu temperature low enough to stop the Cpu from slowing down or switching the PC off.
Some Cpus have different versions with different TDP ratings.
See here for a list of Cpus compatible with your motherboard (all are TDP 95W or less) :-
http://www.cpu-upgrade.com/mb-Biostar/N68S3B_6.x.html
In your question that 965 TDP 125 Watt Cpu would work but if it runs near 100% for long enough (a few minutes) it could get hot enough to throttle back to a slower speed or even shut down the PC. Plus it could overheat the VRMs which would damage the motherboard.
Basically you need a motherboard that can supply enough power to the Cpu and Cpu cooling that can keep the Cpu temperature low enough to stop the Cpu from slowing down or switching the PC off.
Some Cpus have different versions with different TDP ratings.
See here for a list of Cpus compatible with your motherboard (all are TDP 95W or less) :-
http://www.cpu-upgrade.com/mb-Biostar/N68S3B_6.x.html