Hi Murphys Law,
Usually when people say that their newly planted tree is in trouble, its one of three things.
If it's planted too deeply and looks like a telephone pole in the ground, then the tree is stressed. You should be able to see the root flare.
http://www.tlcfortrees.info/planting%20depth.htm
If your tree was rootbound when you planted it, it won't be able to take up water and nutrients. If it looked like this, remove about 2/3 of the soil, untangle as many roots as you can or cut roots to untangle some and water well.
http://msucares.com/lawn/tree_diseases/images/rootball.gif
Regualr watering is a must with newly planted trees.
http://www.watersaver.org/pdfs/fall_watering_trees.pdf
Hope this helps,
Newt