scotchen is right
but also the P4's throttle themself if temps are too high so youll actually know when your system is to hot if it starts lagging alot... as for AXP max temp are more critical cuz you can burn your cpu if it overheat some...
Asus P4P800DX, P4C 2.6ghz@3.25ghz, 2X512 OCZ PC4000 3-3-3-8, Leadtek FX5900@450/875, 2X30gig Raid0