How do you do it? I want to have it so using a teleport triggers a drop in gravity so the player can float the the ground(for a parachuting test map), and then once he hits the ground the gravity returns to normal. And if possible, so it can only be altered for one person or within a certain area.

i will release a para test map shortly. stay tuned

Nerver used it but DoD has this:
http://collective.valve-erc.com/index.php?ent=trigger_gravity

Maybe this can be used by messing with the speed and angle:
http://]http://collective.valve-erc.com/index.php?ent=trigger_push

I dunno ... maybe someone who has used them can help you :D

I thought there was a gravity entity, but I looked again and couldn't find it. I'm using AB's FGD.

trigger_gravity - its a brush based entity, not a point one.

and it is on ABs FDG.

How would I use it, though, still don't know. I'm trying to have it avaliable for one person and on a multimanager so it'll go off after 4 seconds(I have a brush teleport that takes about .5-1 second to hit, and another landing zone to parachute down onto). Right now I have a set of conveyors on {blue set to additive, but it's not convincing and the falls do about 10 points of damage.

Also, will a VIS blocker prevent someone from seeing an area of the map seperated by a skybox? If not, then I could just put it under the map.

Well, my test map is almost completed. Right now I'm just running my final tests on the locational drop, and what luck I had, my height and gravity level was just right, so I have a 9 second drop:D

http://www.dayofdefeat.net/forums/showthread.php?s=&threadid=18047