i was playing l4d for like 4-5 hours (stopped playing an hour ago)

my GPU(9600GT sonic,they oc it, like yours): 40
(q9300 below)
my core0: 54
core 1 and core 2: 45

hdd: 23

for better cooling, you may try some gpu & cpu fans, if your case is too crowded and small, air may not flow freely, so try tidying up inside of the case, dont put the case under the table or something. (You may buy a new large case with 3-4 fans.)

how many fans your current case has? how are they placed? any object blocking them? air can flow freely inside the case?