How do I wipe the hd on an old iMac that is pretty well bricked?
I would suggest, that assuming you can physically--and safely(!), taking note of the comment about voltages and CRTs--removing the hard drive and taking it apart. Most times you can get the actual platters/discs out without too much trouble and carefully smash them. Most are, I think, a metal coating on glass of some sort, so watch splinters wear eye protection, etc. This can be easier than smashing the metal case of the hard drive which might not actually destroy the platter(s).