How to get from Recovery Mode to DFU Mode?

I know the difference between the two modes. I have to get from recovery mode to dfu mode, but i don't know how. My itouch 3G will not boot up, and i need to open it with tethered, but in order to do so, i need to get into DFU mode but i can only get to recovery mode. Anyone know how to get to there? I have done it before, but it is not working for me this time. Restoring is not an option...