Yeah it's the map/background that I was worried about too. It's not "infinate" per say but it would certainly have to scroll as the player moved.
Most adventure game engines allow some scrolling. It's mostly a question of how much texture memory you can use. rpg's reuse a lot of things and so they can get away with larger scrolls. Also, like Erwin said, you could do something of your own where you were constantly replacing sprites as the screen scrolled. At least I think you could, but it's something built into rpg engines.
I know one pretty popular one with multiplayer is Ariannehttp://arianne.sourceforge.net/?arianne_url=content/about
However, you need to be careful with that kind of thing because it tends to be a lot more than what most single developers can handle. There are a few that actually manage to get a game out, but it's a small percentage of the ones that try to do it. A single author really has to consider scope, especially if you're inexperienced. If you're inexperienced and starting out on an rpg, your odds are virtually nil of finishing. That engine has been out for a long time so take a look at how many finished projects have been made with it, then go over to AGS and see how many finished games have been made with it.