Use the pistol in secondary fire mode (right mouse button) to "pistol whip" a German. I don't think you can punch per se. It takes usually 4 pistol whips to kill a German, but fewer if he's been wounded.
Yes, Germans have to reload just like you. When I'm desperate, out of ammo, I rush the rifle-wielding Germans -- they have bolt-action rifles so they need to pause to reload after every shot.
[This message has been edited by Geo (edited January 12, 2002).]