You can als watch this tutorial:

It wil show you all kind of differend doors

If you place the wall a little bit to the right, it will be gone xD

I had a jumppad in COD4. You can still use the same code.

[code]
function jump()
{
   jumpx = getent ("jump","targetname");
   air1 = getent ("air1","targetname");
   air2 = getent ("air2","targetname");
   ...

YES, i was looking for this 

When you are not in a start zone you will die, the game thinks you cheat

works for cod4?