Jens Pulver (the one who got his ass beat down by BJ Penn) demonstrates a nice way to drive into your oppoent for the underhook.
A Clip From:
"Learn to Fight and Win with Jens Pulver Vol 1 - Dirty Boxing"
Jens Pulver, the guy who got his ass handed to him by BJ Penn in their second fight here:
Instructs us on how to shell up and punch your way into infighting range, with an underhook to boot.
This is a short clip, but you can download his entire video here:
I'm sorry, but I just had to put up that first clip-- SOO much shit-talking leading up to the fight.