thanks Quad, good comparison there. incidentally, i really like L4D and am really pleased with my overclocked 9600GT

i'll check out my fans in a minute or so (i'll switch off before pulling it apart and scoping out as much as i can). it's a very, very old case, (much much older than any of the pieces inside it, as this computer has just been upgraded over and over) and i wouldn't be surprised if that's the issue. it's on top of my table, so it should have plenty of room for ventilation but that's no good if the case is useless.

played CS:S until it crashed (didn't take long this time; two short rounds on cs_office) and almost immediately upon loading my temperatures went up (two screens meant i could have SpeedFan visible at the same time easily):
GPU: 66C (up 4C)
System: 46C (up 3C)
CPU: 83C (up 5C)
AUX: 54C (up 20C, and was very sporadic during loading)
Core: 66C (up 4C)

julz

EDIT: one fan on my motherboard, one on my GPU, no others.