hah i never realised lberty city was based on new york... i must be retarded its so obvious... as for the subway, i wonder if you can do stuff on the trains or if you just get on and then appear at the stop you choose?
Well initially, Liberty City was based slightly with New York when it comes to land mass, but mostly it is based on the easy coast theme. The new Liberty City of GTA4 is based completely on NYC.
As for the subway, I bet it gonna be like it is on real life...you get on the train, and wait for it to go from stop to stop, the hud/map will tell you where are, and you get off at the appropriate stop.