This only works in co-op.  DONT USE ANY GRENADES.  In the Beginning the first you thing is when you get the Warthog and you drive to that platform where you have to get out of the warthog and go into the building where the door is locked.  Pick up as many grenades as u can.  Then you keep on driving the warthog about 60 hards off the platform and you should run into an overshield.  DO NOT PICK IT UP.  You should have 8 grenades each by now.  Stand on a spot right near the overshield, about 10 yards from it.  Have your friend smack you so all your grenades drop.  DO NOT PICK UP YOUR GRENADES.  Do the same to your friend.  Keep doing this and getting more grenades till theres about 20+ grenades.  Now, get the warthog and park it directly over the pile of grenades.  Have you or your friend get a plasma grenade, JUST 1 NO OTHER GRENADES.  Now, stand behind the overshield.  Have you or your friend throw the plasma grenade into the pile of grenades under the warthog.  Right after he does this, run into the overshield and get in the warthog.  THE OVERSHIELD MUST BE CHARGING FOR THIS TO WORK.  When the plasma blows, your warthog should go flying really really really really really really really really really really really really really high and maybe land on top of the level.  If this happens, get a checkpoint and have fun jumping off the cliff.  Enjoy!

Another fun thing to do is make a big pile of grenades, then park a warthog about 20 feet away.  Get in the warthog, and have your friend throw a plasma grenade.  Drive into the pile right as the grenade explodes, itz awesome.  You have to time it right, though.

To get on top of sidewinder you need to get a tank across the bridge.  The bridge is one of those cliffs where you can get the rocket launcher except you have to cross a bridge to get across it.  Anyways, have you and your friend each get a rocket launcher, 1 plasma grenade, and 1 frag grenade.  Throw the plasma, then throw the frag, then shoot a rocket.  They should all blow up at once, and keep doing this until it's on the other side of the bridge.  Now, there should a rock to your right.  Back the tank to the left of the rock, so itz about 7 feet from that little cave.  Get a ghost and fly off the tank and you should be on top.  If this doesn't work, reposition the tank until it does.  To get a warthog on top, go to the other side of that cliff and park a warthog there.  With your friend at the same time, throw a frag grenade then shoot a rocket, and the warthog should be up there.  Have fun!

Not a high quality pic, but it shows wut itz like up there.

 A video of how to get on top of the silent cartographer-

If you can't quite reach a ledge, try grenade jumping.  To do so, point your gun cursor thingy all the down on the ground.  Then throw a grenade.  When itz about to blow up, jump, and you should get about 7 extra feet of air, at the cost of half your health.

-Target practice. In multiplayer, allow all vehicles in a map(sidewinder or BG). Have Rocket Launchers. Have a player be in a Ghost or a Warthog(Ghost is better), and another with the RL. The player in the Ghost will get air off a Scorpion Tank, and the player with the RL will try to shoot the Ghost out of the air. If you can hit that spinning Ghost, your aim is excellent. This improves your accuracy and ability to lead targets, especially with the RL.

~Halo 2 I got an unfrickinbelievable kill.  21 kills in a row without dying.  That game i got 38 of my team's 50 kills.  Good times.

~Getting on all the maps in Halo 2

~Gettin on top of the Map blood gulch

~There was a blue elite and a red elite lined up, and i took out my sniper and bam, one headshot, two elites down.

~When you kill an elite, all the grunts run away waving their arms.  This happened, and all the grunts were running away right next to eachother, and i took my sniper, and BAM, grunt down, moved my sniper to the right, BAM, grunt down, moved my sniper to the right, BAM, grunt down, moved my sniper to the right, and BAM, last grunt down.  I did this in single player heroic on the level Halo.

~I was playin computer Halo Trial with conner, and conner was in a banshee, chasing another guy in a shee.  I wuz in the gunner seat of a rocket warthog, killing people, and on the other side of the map i see two shees.  I say oh wut the heck and shoot a rocket over there.  Conner is just flying around, chasing the other shee, and he sees a dark glow coming for him.  By the time he realizes it wuz a rocket, it'z already hit him.  It was probably the funniest and luckiest thing i've ever done in Halo.  And of course, in a game of 16 people, I hit CONNER.

~Gettin on top of Silent Cartographer for the first time

~Gettin on top of Sidewinder for the first time.

~Warthog races with michael

~Gettin on top of the blood gulch base for the first time with matty

~lotz more to come

Make a gametype with 400% health.  To get on top of blood gulch u need to go near the( I think itz red base?).  U get a tank and put it on the slope on the right side.  Itz near the big peak on the map, the highest point.  Get a ghost and have someone tag the back of your ghost, then quickly fly at the tank, go off it and then u go flying  when the grenade blows up.  when the right side of ur ghost is facing the top of the map, get out and u should go FLYING up there.  If you wanna get a warthog up there before you get up there have u and ur friend throw a plasma grenade, frag, then shoot a rocket right behind the warthog when itz near the same slope that u parked the tank and it should go FLYING.