What CPU and GPU so you have in there? We can look up the safe temp threshold on a specs page. High 80s °C for GPU is a safe level....I personally don't like them to hit 90°C or above, although you would have to push it over 100°C to kill it.

CPU - AMD I don't like my X6 to go anywhere over 60°C under 100% load. Mid 50s is better.
Intel - depends on the chip - the new S.B. is rated quite high, and Dad's crunches in the mid 70s or so just perfect.