I think I'm going to try the suggestion of powdered laundry detergent first, then if that doesn't work (it's a big mess) I might go on to more aggressive approaches. I also had a similar thought to putting down a skim coat of concrete, but putting it on dry. Ooh, or... tell me if this sounds ridiculous.

Mixing a little bag of quikrete with mineral spirits instead of water, but mixing it thick so it has room for more moisture. Then spread it over the floor, hoping that the mineral spirits (or maybe turpentine) dilute and soak into the oil enough for it to become viscous, then soak into the quikrete and solidify. With the coat being that thin, it should sweep right up. I'm thinking that I should call my friend who's a chemist for Eli Lilly to verify my theory. If it works, then I'm totally taking out a patent on it .

(by the way, the reason the floor is so bad, is that I didn't get a decent seal on the transmission fluid pan before I filled it up, and every drop drained out of it. Of course the car was on jacks and I didn't notice until it was all over the garage, and had been seeping in for a month. SUCK!)