Yes. If you have installed at least one game from The Orange Box, you can use Garry's Mod.
no you cant but if you buy Half-Life 2 for PC you can get Gmod and mod the game ect.
You cant. It doesnt come with The Orange Box.
if you have bought garrysmod on its own then that is your problem, you need to have another game to back up gmod otherwise you will have missing textures, ragdolls and guns, to solve this go onto steam and buy half life 2 or the orange box pack
Blueray is backwards compatible with DVD and CD so yes.
I think you can use portal in gmod 10, but I'm not so sure.
It is compatible with every game in the Orange Box.
Yes, you must.
runOnTick(1)
I belive the song was Miracle from Cascada but the part of the song from the gmod episode is in the middle of the song.
If you want to make models for gmod look at XSI Mod Tool.
download them from garrysmod.org
Get a new PC.