DFU software?

Is there any DFU software for mac? I have looked everywhere and can't seem to find one.

Reason being, I can't seem to get my iphone into DFU mode so I can downgrade my 3g back to 3.1.2
If anyone can help, that'd be great.


Thanks


(Edit: Yes, I have tried the home and sleep button thing like a hundred times)

Nevermind! It seems that youtube was wrong...pretty much the entire time.

http://www.redmondpie.com/downgrade-ios-4.1-to-ios-4-3.1.3-3.1.2-how-to-guide/

That link above is for anyone else with the same problem I had.