"When I bought my case it came with no fan other than the one in the power supply which for when I got it was quite fine. That was with only one HDD and one CD-ROM and only a graphics card. But as I advanced into the fields of overclocking and hardcore gaming it found that computer temperature inside my case what rising quite a lot!
Well my first step was to get a 80mm fan for the front of the case. Lucky the case I bought had pre-drilled holes in the case having no screws with the fan that I bought, So I just got some green garden twist ties and tied it around the holes in the case and then to the fan. The fan came with a plug so I could plug it straight to the psu (Just like a cd drive)."
FULL STORY @ NETKILLS (http://netkills.qgl.org/a_casecooling.shtml)