No, you need iTunes to copy music files to your iPod (I personally like iTunes). And, I'm not completely certain, but iTunes may convert the music files to m4p before transferring them to your iPod, but if you're managing your file manually, the ones on your computer should remain mp3s.

There is a setting in the iTunes Preferences to do this:

Edit>Preferences>Advanced:

Uncheck the "Keep iTunes Music Folder Organized" and "Copy file to iTunes..." options.

Tim