Welcome!
So far I've only messed around with AGS I've made one free game and I'm finishing up another commercial project. When that is done I want to create something along the lines of Runaway. 3d characters w/ cell shading in a 2d environment. Help me get started.
Actually there IS no change, maybe you misunderstood the making of Runaway the same way I did. You are right - the Runaway characters were constructed in 3d and rendered with cel shading, BUT they are PRE-rendered in the game (with a a really high amount of frames per animation), it's no real-time 3D rendering.
(Yes, I am sure about this - now! ;-) !)
So finally Runaway uses the same methods as you are used to. The shadows are possible due to alpha channels, Brassfire already mentioned. To reach your goal, you have to construct your character animations in e.g. 3ds max 5 (which has a built-in cel-shader!) and use the rendered frames as you are used to in your 2d environment.
WME seems to be a good choice for that, I already tested this method with alpha channels and it worked fine and fast.
Oh - what game did you release, something we can have a look at ?
Greetings, Jerrot.