Natalie said:
They actually suggested that I grow it in a pot, and move it indoors every winter, but that isn't something I am willing to do. 
That is THE most rediculous thing I have ever heard with respect to a Crape Myrtle. ABSURD. Who supplied this plant?
Bringing in a 12 - 30 foot tall tree indoors? Preposturous. Aside from the fact it would likely die. Even keeping it in a pot, it would likely get 10 or more feet tall.
In terms of location, being a South window, I would not put it right in the window, but perhaps off side a ways so it gets a bit of indirect light. While it likely will not freeze, there is still a risk of very cold - thaw - very cold - thaw if kept in the direct sun from the window. That for a plant is killer and a reason for sinking pots rather than just sitting them on top the soil..
I hope I indicated I am winging it here as well, cause I never wintered over a Crape Myrtle inside, nor in general would I.
Last year about this time I bought ~ 7 shrubs from Earl May and 10 4-6 " pot Perennials @ 2 $ each. Big time sale - $5 each for shrubs that listed for 30 - 70 $. I brought them home, dug trenches in my vegetable garden, sank the pots, watered them in and piled 2 feet of leaves and straw over them. That is my preferred treatment for very late season potted plants if it is too late to plant.
