Case cooling will definately help.
I just got my 1.1 Ghz system and after playing Unreal for a few hours my temp was 36C Mobo and 55C CPU. I then removed the thermal pad with some thermal goup, replaced the CPU fan with a quiet panaflo, put in a slot fan and a 80mm exhaust fan and my temp went down to 29C Mobo and 44C CPU. Planning on adding an intake fan and that might lower it a bit too.
Also try to lessen the voltage if you don't plan to overclock. I can lower my voltage to 1.5 and still run stable, that will certainly decrease the amount of heat released.