Make sure you have portal installed on steam, then start up garrys mod, and go to Extensions, switch to the game content tab on the right and put a checkmark in next to "Portal". Restart Garrys mod and you will have the content for Portal available.
Garry's mod is a Source Engine Conversion, on which Portal is based on.
Garry's mod can take models (and textures, correct me if I'm wrong) from Portal and use them in itself. However the ASHPD Isn't useable. Which makes me sad too.
Yes, garry's mod will work with portal and you will have all the HL2 stuff.
In order for Garry's Mod to work you need a minimum of one Source Engine game eg. Half-Life 2, Team Fortress 2 or Portal.
Garry's Mod is only for Valve-released games, so no.
Buy Garry's mod 10 off of steam.
yes
technically yes, there were a few updates it is still called Garrys mod 10 though
Garry's Mod 10
You do not make an account on Garry's Mod. You need something called Steam. http://tinyurl.com/2vwrgf5
own a server or ask the owner to make you admin
It may work but it will be extremely slow and likely to crash a lot.
no because garrys mod requires that you have a game that uses the source engine
Garry's Mod has now updated and includes all features of 13 Beta