For those of you with fresh, live Christmas trees, this is what to do with them:
When you get your tree home saw off the bottom inch of the trunk with a nice fresh, clean cut. If you don't have the means to do this, ask the guy at the tree lot to do it when you buy it. He should do it cheerfully. If he doesn't, he's a grinch, and you have my permission to pay him in coal.
When you get your tree home with its nice, freshly-cut trunk, put it in water right away.
Crush up a few aspirin (it must be aspirin, not tylenol or anything else. ONLY ASPIRIN!) and drop them in the water. This keeps the xylem open so the tree retains its capacity to uptake water better.
Keep the tree well-watered. Check it every other day and top it off as soon as it starts to get low. You will notice that at first your tree sucks up loads and loads of water, and will probably need to be refilled every other day, or possibly every day, depending on the size of your reservior. After a few weeks this will drop off, and you will notice your tree going through less and less water. When this starts to happen, add some more aspirin.
Keep on the aspirin and water and your tree should stay nice and fresh and full of needles for several weeks.
Oh, and try to keep your tree away from direct heat. Don't put it near a heat vent or radiator, or, if you can't avoid it, turn off that particular vent or radiator and turn another one up a notch that is father from the tree.
This message brought to you by Prof. Duh of the University of the Bleeding Obvious.