Slim the Cat is on his last legs -- help help help!

15 years ago a feral cat named Spiderman snuck into my postage-stamp-sized back yard and gave birth to four kittens. The other three kittens were soon socialized and went off to good homes but Slim was always a scardy-cat and wouldn't let anyone touch him. So him and I easily bonded -- I was that way too and understood him perfectly.

For the last 15 years, Slim-the-Cat and I have rubbed along just fine. For my part, I've put out food for him twice a day. On his part, he has refused to let me cuddle him and has avoided tracking cat hair and fleas into my house. It was a relationship made in Heaven!

Then Slim got cancer. Then he got attacked by a raccoon. Weighing only around four pounds and looking like Skeletor, I figured it was time to put him to sleep. So I fed him a whole Tylenol with codeine cleverly concealed in some fabulous raw tuna and he ate the whole thing. Nothing. The freaking cat didn't even stagger. That dose would have knocked me out like a light for a week. Hummm. This cat really wants to live.

So then I fed Slim some steak and while he was occupied with that lure, I snuck up behind him, scooped him up, put him in a box and closed the lid. "Slim, I got you now!" No I didn't. Using super-strength that he got from who-knows-where and using his skinny pathetic cancer-ridden raccoon-scratched-up paws, he clawed his way out.

I figured that if anyone wanted to hang onto life that badly, who was I to play God. So I gave Slim-the-Cat a reprieve and a chance to die peacefully in his little postage-stamp-sized backyard domain.

That was four months ago.

Caution: Do not read this next part unless you have a really strong stomach.

Since that time, Slim's ears have rotted off and his nose has rotted off and half of his tail has rotted off and he is all infected and filled with cancer and pus. This is a Hall-of Horrors-looking cat. But underneath all this grossness, he is still the same, sweet Slim-the-Cat. But enough is enough. "Slim, no matter HOW badly you want to hold on to life, you really need to be put out of your misery."

So here is my question: How do I go about doing it? What should I do? And HOW do I get the courage to do this to my old friend? And please please please, while you are down on your knees praying for our brave troops in Iraq and that somehow America will someday have sane people who are legally elected living in the White House, also please pray really hard for Slim-the-Cat.