This is a jump height changer that works on live servers! I made it so that you can mess with the value, but I recommend the default one for just messing around in goldshire or something.
http://dls.vivec45.com/wow/hacks/2.4.1jumphack.zip
EDIT:
Safe as of April 03, 2008
Guide, as requested:
Download the zip file.
Unzip the zip file.
Start the " .exe"
Go in game.
Hit "CTRL+1" a few times.
Jump.
Also, heres a few values
OFF: 3237909464
On medium: 3247909464
On high: 3249909464
On super: 3250009464