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information that go on your compuer
It means its cracked (you can play it for free)
DO you mean on the PC, or on a console? On the PC, just like with the other games. For the Wii, there are no stairs. Not sure about other platforms.
By co-op you mean mulitplayer. Yes. Half-Life 2: Deathmatch is only on PC.
The USB is the little port at the top of the PSP, which can be used to connect it to a PC.