How can I do this?

I saw this glitch where someone got into a crate near BL spawn in Port MM. Can anyone tell me how it's done?
[img]http://i686.photobucke*****m/albums/vv221/Idedu/Crossfire20100221_0007.jpg?t=1266807641[/img]

Yeah, somehow you corner glitch in, then go to the very edge by the ramp so the area doesnt kill you,, theHuhnfisch has a really good tut on all the glitches in zombie mode

Here ya go... just do exactly what it says, it works pretty well... just be careful because some boxes kill you when you are inside.