I have a tower case with 6 5.25 bays and 5 3.5 bays, most are full. Cooling is a bastard, I can no longer get a 1200 athlon to run in my system without burning out rather quickly. I have been through 3 1.4ghz athlon XPs and 2 1.2ghz Athlon XPs, I cant afford to burn out any more chips so I am only running the processor at 850mhz
I have the biggest fan you can get (a huge coolmaster) with more than enuff heat conductive paste between heat sink and processor, My case has 8! yes 8! big powerfull fans, the front ones blowing cold air into the case and the back ones blowing it out, but still the ambient temperature within the case is very hot!