Pick up some 2 sided tape, you can get it at a auto parts store, but I've found that the wider tape from Radio Shack holds better... Just clean the surfaces with alcohol first and let air dry..
I've got 9 fans total in my case ( 10 degree's F above ambient case temps, highest CPU temp with 2 hrs of benchmarking was 107 till the smart fan kicked up the RPM's then drops back down to 100 F, I'm anal about heat ), and most are attached with tape.. Most fans that you buy have a plug that will plug into the HD power plug to tap for power.. If not just strip the wires back and push them into the back of the plug.. Black to black ( some are blue to black ), then red to yellow.... If your wanting a case fan, get atleast a 80mm fan, you can get bigger ones, and thats what I'd recommend.. Unless you like a quiet comp..