Try and make a Air Pathway. Also Try to keep the presure (sp?) in the case even with the presure outside of the case but if this is not possible try and go negitive. to tell if it is possitive or negitive look at the CFM rating of the fans and have the CFM even going out (fan blowing out the case) with the CFM Going in (fan blowing air in case.) (Yes, I know I probibly used CFM incorectly as a term. but I cant Remember what it stands for. its like Cubic somthing Meters.) Also you need to remember that Hot air travels up. So if you want effective cooling get some powertools and cut a hole in the top of the case and have a fan blow air OUT of the case. (blowing in just does not make sence to me as getting rid of hot air is easyer then trying to cool it off, + colder air from the bottem moves up.)
SVC has some Great Prices on cooling fans and stuff. Bigger fans will have Higher CFM/DBA (DBA is noise level mesurement) You want a low DBA. Also I recomend geting the Panaflo fans. They are quiter then rated ive been told, and have a good CFM. And then you enter the Cold, EVIL, trade off of CFM for lower DBA.