hi raimund (klingt ein bisschen deutsch)
it's possible that the cpu died, but let's think about other possible problems.
does it anythig besides the starting fan?
does the hdd makes any noises?
what about the optical drive?
it's possible to place something inside the iMac - but the only thing what stays "mac" will be the casing - the lcd panel, the optical drive, the hdd - everything will be removed.
surely it could still be far less expensive than a new mac - but that depends on the used hardware.
those "hackintoshes" are almost working like the original ones (also depending on the hardware) - the board i've got for my iMac g4 project is from an aopen digital engine - it has 2 vga out, hdmi out, 4 usb 2.0 and so on - i cloned an 10.6.3 installation on a new hdd, installed chameleon and that was it - the easiest "hackintosh" i ever made ;-)
the only problem is the osx eula! (but since i own a few licenses - i don't care & they have no chance to sue me in germany)
there are many possible ways to get the job done - some are not that great - and others work like a real mac - the only difference is the missing apple EFI on pc boards, but thats why i use the chameleon bootloader