This might help

http://gonyc.about.com/cs/christmasinnyc/p/holidaywindows.htm

If you're lucky enough to use live branches, the smell is wonderful. I always use paper doilies. Cut them in half, dampen with water just enough to make them stick to the window glass,and then spray with artificial snow in the can. You could also use white shoe polish, I find it doesn't have that smell and fumes, and it's very easy to wash off. It doesn't flake off like the fake snow either. They also make paper lace and you could try that,too. Use fishing line to hang some pretty snowflakes from the top of the window. They move slightly in the smallest breeze. Hang 2 on one string, 3 on the next,keep alternating. Use a wooden trunk or box, to display some antique and vintage toys, or place them under a tree. A train is always wonderful, a small picket fence,create a curtain of lights from mini twinkle lights to hang behind the window display. Use tinsel garland cut in different lengths and hang a Christmas ball on the end of each in the top of the window. Use a chest or dresser to display items in the drawers. Or an old baby carriage or cradle. Have the children in your family help make the classic paper chains. String popcorn and cranberries.
It'll be great!

Here is a link that might be useful: Kudzu's Blog

There was a similar thread to this but about fall decorating. You may get some ideas that can be changed up for winter?

Here is a link that might be useful: Fall Decorating Thread

Growing up 1 store in town decorated 1 window like a toy shop, every yr I would just stand & stare at all the pretty stuff. So a toy store in 1 window, maybe a "ladies" window-gloves, sweater, necklace,coat, magazines, a men's window, all with some of the snow around the edges & bits of gold garland around for little bling. I make my front window an antique store window each yr. Tiny xmas tree, little cars, small dolls, minature books, 1940's donkey cart,teddy bear. An antique store with windows is great way to show those who would never dream of going in what wares they have.That would be dream job decorating that. Hope there is place to lay things & not just windows but if just windows they can put items on top of a bookcase, table,bedroom dresser etc. Tell them if they use something like that to have a nice attractive sign hanging off the item down lower so people know that item is also for sale. Sign could say,Santa's Special! Bookcase only $20. Jan

These are all great ideas, thank you so much.