Is it possible to pause GTA IV (PC version, via Steam) during cutscenes? And if so, how?
Apparently, if you have patch 184.108.40.206 (Title Update 2) or above, the cutscenes pause if you ALT+TAB out of the game.
According to the changelog from this link. (click on "Click Here To Show More Patch Details").
Universal Pause Button can be used, the program freezes the game process. Hotkey can be modified.
Please note that a paused program can't recover if the foreground window is changed - "unpause" first.