For the switch and case statements, check this:
http://library.thinkquest.org/C0111571/manual.php?tid=13)
In the .dlg file, you should see small boxes named P1, p2, P3, P4 , P5.
If you look at c_mand_planet.nss you should see the following line: int nPlanet = GetScriptParameter(1);
It refers to the first box (P1) . So just attach the script as you would normally do in the conditioanl script field and type the number for the planet you want in the P1 box of your .dlg branch (Telos would be 2).
Look at mandalores .dlg file if you want to see it in use (Entries 60, 63, 67, 69, 71, 73, 76)
The explanation is a bit messy but it's pass midnight here :p