How do you trick jump in halo 3?

[dan]

Ive seen these videos on youtube. Here's one of them:
http://www.youtube.com/watch?v=6ViVoFgtUgo&feature=channel_page

They are amazing, I want to try them but don't have any idea how.
When they throw grenades in the vid they somehow dont die when they bounce of them.
Also why do most of the players have pistols when jumping?

 

[Sexy beast]

The reason they have pistols iz bcuz they cant fire machine guns while jumpin

 

[KevinTheGamer]

Read this
http://digg.com/xbox/Amazing_New_Halo_3_Jumps_Discovered
http://www.mmospot.net/forums/