kel,
You will have to re-download it again from blizzard, or go to any game seller (best buy, Game Stop, etc) and buy the demo CD for a couple bucks.
You can also get all of the latest patch files from here, so you don't have to use the blizzard downloader to get previous patches:
http://www.blizzard.com/support/wow/?id=aww01810p
Valdor