Cooling isn't going to change anything about the performance of a game. The only things I can think of are opening task manager (ctrl+shift+esc) and setting the game's affinity to one core and running the game in windows mode (which can often be done by hitting alt+enter). Other than that, google for stuff like "dawn of…
Yeah cooling can make a huge difference, try open up the case and blow a big strong fan directly onto the components while you run Dawn of War 2 to see if that makes a difference. A word of caution though don't do this (or be very careful) if you're CPU cooling system is one of those duct type systems and doesn't have it's…