If you're only as far as having gotten the Dark Beam, then I can tell you that you won't be able to get rid of that door for a long while.  You'll need the charge-missile-thing, where you hold down the missile-button, manual-aim to highlight each target, then let go to fire off five missiles in a row.  That won't be for a while.

I can't think off the top of my head exactly where you are....but you shoulllld be able to avoid that area for now.  I think you need to at least get more keys for that area, and if you don't have it by now, search for the Light Beam, because you get that pretty soon after Dark Beam(I think...it's at least before the first boss).

This is the thing I hate about this game: the objective is always the same...look for keys.  They do it the same every time too: scout Light World until you find the Temple, talk to dead-hologram-guy, break your way into the Dark World, gather three keys(sometimes fighting mini-bosses), open up boss area, beat boss, get energy from temple, return to light world, restore light-energy to temple.  Every time.  -_-;;  As far as typical Metroid games go, it's the farthest removed from the usual series in my opinion.

I'm not sure where you are or how many keys you have left to find, but they're all in the Dark World, so you have to deal with that place.  It's a good idea to break out your map and look around for suspicious areas, although I don't know if they really pop out all that much really.  I can 'see' a few areas that I remember where they are, but I don't know their exact location...just that one is in a sort of 'cul de sac', dead-end cavern where you'll battle some guys, and I think one or two are just in a previously-high-place that you can lower by shooting a panel with a light or dark beam, can't remember.  Not sure about the third except that you just have to scout around, looking for areas you haven't been to yet and sort of inspecting them....*shrug*