I've never practised Chaos Magick, but I've read a bit about it. Apparently, Austin Osman Spare (if my memory serves me correctly) was a contemporary of Aleister Crowley. At first, Crowley found him quite fascinating but, after some time, ended up denouncing him and throwing him out of the O.T.O. Spare went on to develop Chaos Magick, which is essentially a form of auto-sex magick with a personalised alphabet involved.
Sex Magick is, of course, tantric sex modified in a manner that purportedly uses the libido (kundalini energy - if that's your bag) to affect change in the external environment. Both tanric sex and sex magick claim to put you in touch with higher powers, while the former will apparently make the connection between you and your partner much stronger (I do subscribe to this) and more in touch with the world around you; the latter will supposedly do the same thing, while (again, supposedly) allowing you to affect change in the "outside world" through the manipulation of this energy.
I discovered Crowley while reading a lot about tantra and yoga around ten years ago. While he was undoubtedly a complete and utter nut-job, I found his writings on the above two topics far better than traditional texts. His writing, in these instances, is clean and pragmatic without any spiritual hoodoo (Ex. Book IV). The rest (save for a few interesting philosophical positions), however, does require a tinfoil hat.
Back on topic. This is all I remember about Chaos Magick. I can't remember who it is, but there is at least one person on this forum that knows a hell of a lot more about Crowley than me. I would assume that they also know a lot more about Chaos Magick. Jamshyd, maybe? Willow? Erm... I can't remember.