How can I wire an HD antenna into my attic?
There's no substitute for it:  You're going to have to fish that wire.  A couple observations:
1.  If you were the "cable guy" you'd probably take the easy way out:  Drill from the living room through an exterior wall, then go up the outside of that wall.  Pretty cheesy, but common enough that people pretty much accept it without much question.  I'd recommend against it, since you don't need any extra penetrations of your exterior walls, but it is commonly done.
2.  The right way is to fish it up an interior wall or chase:  You could cut into a wall, fish the wire, then repair the drywall.  Or you could run it up a corner and make a mini chase by covering the wire with some kind of molding.  Or you could run it in a surface mount wiring tray. I've even seen some people get pretty creative with removing door molding and running wires in the space between the jamb and the framing, then drilling up through the header to get through the ceiling.  But I wouldn't recommend it, because you'll more than likely weaken the header when you drill it.  What this all adds up to is, unless you're feeling pretty ambitious, you may want to call in a pro.

Edit after all this typing:  There are TV Tuner-over-ethernet products out there.  Perhaps you put the antenna in the attic, put the TV Tuner sending unit up there, and put the TV-Tuner receiving unit in your media cabinet.  Whereby you can ignore my entire first paragraph.  :-)