i dont know about other systems, but i was just running some tests one of mine... xp3000, 500wat psu, 6600gt.
temp of the room = 65F, 18c
with case fans... \case temp = 28c \cpu temp = 35c, max load 44c
without case fans... \case temp = 38c \cpu temp = 45c, max load 54c
so in my system, case fans make a big difference. it may do the same in yours. if its just overheating, you can take off the side pannel and jus blow a fan tward it to test.
temp of the room = 65F, 18c
with case fans... \case temp = 28c \cpu temp = 35c, max load 44c
without case fans... \case temp = 38c \cpu temp = 45c, max load 54c
so in my system, case fans make a big difference. it may do the same in yours. if its just overheating, you can take off the side pannel and jus blow a fan tward it to test.