It looks like func_door isn't in the Portal 2 SDK, so I'm kind of at a loss for how to make a sliding door activate on a button press. prop_rotating_door is still in, but unless there's a way to make that just slide, I can't use it.

func_door is a base Source entity. It's in every game. You realize it's a brush entity and not a point entity, right?

Wow, now I just look stupid. >_> It's been a while since I've used Hammer and I forgot how to make brush entities. I figured it out, though. Thanks! : D