Always snap to grid
Legacy:Gravity, Warp Tunnels
Make these types of things in UnrealEd is quite easy, and I'll attempt to explain it as quickly and concisely as possible. First of all, I'll assume you already know about Zoning. Now that we've assumed that, go into your actor browser under Info.
Getting Set up
Add a ZoneInfo (just plain "ZoneInfo", nothing fancy") into your map in the appropriate zone (the one that you want to have different gravity or velocity effects).
Now go into that new ZoneInfo's properties. Under the "ZoneInfo" tab inside its properties, you shall find settings called "ZoneGravity" and "ZoneVelocity". Zone gravity is just that - the gravity of the area. It starts at -950.00Z, and 0 in the X and Y axis'. What does this mean? You're moving downward (hence the minus sign) 950 units at whatever rate the editor uses - the standard UT gravity, which I'm sure you're familiar with. Turning it to, say, -450 would allow you to jump over twice as high and fall half as fast. The X-axis refers to the horizontal plane, and the Y-axis refers to the vertical plane, from a bird's eye perspective. Setting these to plus or minus would pull you in that direction in that plane. Note that with ZoneGravity you will always run at the same speed, etc, unless your feet leave the ground - in which case, your gravity settings will influence the player's movement. More technically, gravity only affects players when they are in Physics state "Falling".
ZoneVelocity, unlike gravity, automatically shoots players in whatever direction you say, but it works the same way. There is not much distinction between gravity and Velocity, as far as I can tell, but they do interact with each other - look at CTF-HallofGiants, for example. You can use these in conjunction for more realistic gravity effects, or you can use ZoneVelocity to create warp tunnels (separate your warp tunnel into several different zones, and use a ZoneInfo in each zone with the ZoneVelocity property set to appropriate levels, and your players will be shot through it at whatever direction you've chosen, assuming you set the XYZ velocity properly).
Tip: to make dynamic water, you can use the following settings as an example, ZoneInfo -> ZoneLight -> TexVPanSpeed = 7 correspond to WaterZoneInfo -> ZoneInfo -> ZoneVelocity -> Y = 100 (for instance, a river stream) -Gui
Wrapping it Up
This should give you some basics, but I can't tell you everything - just work off of what you've learned and experiment, experiment, experiment. Eventually you'll figure it out, but as with all XYZ coordinate systems, you'll still be experimenting a lot.
Balu: If I got the two above sections correct there is a very big distinction between gravity and velocity. Gravity doesn't move you if your feet are on the ground, but you get moved in a Velocity-Zone. So e.g. if you'd have a wind-tunnel with a big fan at the end and want to make that move players around the tunnel you'd have to use velocity. (which let's me think of nice traps - Can you trigger Velocity/Gravity on and off? ;)
Jeeptrash: As far as gravity vs velocity goes- you can be moved in one direction by gravity with your feet on the ground: +Z, aka up. I have a zone that I wanted to use gravity in a horizontal direction in, so I set the +X gravity that I wanted to have, and then set Z to +8... just enough of a lift to get the feet off the ground.
You may have read elsewhere that jumppads can be flaky when used on bots. I've found that all zoneVelocity is flaky with bots, which I assume most peoples jumppads use. I use zoneGravity instead and tho its not perfect its much more reliable.
Luggage: Someone should point out that ZoneGravity gradually accelerates players until they reach the specified TerminalVelocity, while ZoneVelocity adds the set velocity to the players instantly.