I agree that the iMac 333MHz is a, well, rambunctious little machine.
I had to put a clear piece of tape over the CD-ROM's button to keep it from rattling like crazy when I had a CD in there
As for the fan, you should be able to replace it with any 80mm (8CM) PeeCee fan, although I'm not sure what kind of power cable (Molex or 3-pin mini) it uses.
-TritiumOSU