Toph,
Don't assume that because the heatsink is just warm that all is well. With heatsink compound its normal for the heatsink to be WARMER because the compound displaces air, which doesn't conduct heat well. Remember its a three step process, transfer the heat from the CPU to the heatsink, transfer the heat in the heatsink to the air in your case. Thirdstep, transfer the hot air in the box to the outside.