REMEBER: always backup your maps for in case your doing something wrong!!!!
Step 1: Download and Backup Some Stuff
Halo Map Tools: you can download it here
Halo Map Swithcer: you can download it here
Step 2: Backup
if you did something wrong and want the original stuff back open up HMS and click on "Restore All Maps"
Step 3: Tune Your Warthog
now youre opened it you see a list, scroll down to Vehicles and click on vehicles\warthog\mp_warthog
On the right side you see some "parameters". Set Top Speed (forward) to 0,8 (put a , not a . cause if you do a . it won't work) Set Top Speed (Reverse) to 0,4 set Acceleration to 0,0099 and Left and Right Turn Angle to 25 and -25
Now search for Physics in the list where you clicked Vehicles. Choose vehicles\warthog\warthog
set Gravity Multiplier to 2 or less.
exit HMT (you dont have to save anything)
Now start Halo and choose Multiplayer and choose for the map Bloodgulch, get in a Warthog and if you done right enjoy =)