When I light up the fireplace, the room is filling up with smoke.
I've checked the flue and it's definitely opened as far as it can go.
What I'm wondering is, is it possible that the chimney, or the pipe
leading up to the roof, is partially clogged? I've heard others
mention too that it could be due to the air flow outside, causing the
smoke to drift inside the house.

Also, the fireplace has what appear to be transparent doors on it (I'm
guessing they're glass, but not sure). Is it safe to close these
doors while the fireplace is lit? I just didn't want pressure to
build up or something weird to happen.

If the chimney/flue/pipe (whatever it's technical name is) is clogged,
what are the solutions? I've heard something about special logs you
can get for the fireplace that help clean out the pipe, do these help?
What do I need to repair this?

Thanks,
Dustin