No personal experience that would be helpful, but here is some reading:

http://www.2ndchance.info/aggressivecat.htm

http://www.heartofminnesota.org/pdf/aggress.pdf

http://www.thecattherapist.com/behav...essive_cat.htm

Check out redirected/displaced aggression. Maybe the other cat or something else in his life is causing the cat to act out, through frustration. Or maybe he just thinks its fun.

I hope that you don't have to put him to sleep. I'll be keeping him in my thoughts.

If all else fails I'd recommend a decent animal behaviorist. You can call your vet and see who they recommend.