its near impossible to fry a cpu nowadays mate...
the mobo will not allow windows to boot if the overclock is ott ;)
Ofcourse, If you overclock it to much then you can fry it!
If your overclocking your CPU then you want to do atleast 400Mhz or you really wont notice a difference, Google your cpu for overclocking to check what sort of overclocking they are getting and copy theirs with like 10 under. This way your secure. Overclocking avoids warrenty.
I ahve my 2.4 x2 @ 2.7
overclockin is so different now... I remember my athlon xp and all you needed to do was up the fsb
now you have to alter the volts etc
yes there is a limit to what you will get from them
if the mobo cant handle it it wont boot so you know you went 2 far