I have a 50's California bungalow; it's largely lacking in those little details that make a house have some character/charm, and I personally feel that one of those things that is missing is trim around the windows. They're basically just holes cut out of the wall -- no sill, no trim. Currently the windows are vinyl (and are going to stay that way; we can't afford to replace them right now, and they're relatively new), which I would imagine are replacements for the original aluminum windows that some of the houses in the neighborhood still have.

So my question: is it possible to add a sill and trim to this kind of window? I have no idea what the jambs are made of -- they've been painted to be the same color as the walls. But is it possible to put a sill on top of the bottom jamb, and then trim around the window, and paint appropriately? Or would it just look tacky?