What to do in Salzburg?

Hi all,
I'll be spending 4 nights around Salzburg in December. Any suggestions on the best things to do/see/stay during this time? I'm wanting to spend some time in Halstatt during this time also.
Thanks.

Sights: [http://www.salzburg.info/en/]
Hotels: [www.booking.com] has about 128 hotels for Salzburg

if you are there between xmas and new years (as i was last year), be sure to book a place for dinner if you see something you like the look of...
never thought I'd go to Salzburg and eat McDonalds for dinner... i did it by the river so at least the scene was nice!!

With a few days you could check out the Mozart Houses, take in a Marionette Opera, go out to the Hellbrunn Palace Trick Fountains.