It will have DVC previews at the end of January, but the official opening is going to be in April 2006. Most likely it will officially open on April 22nd (AK's birthday). Look for soft openings though between January & April.
“You can design and create, and build the most wonderful place in the world. But it takes people to make the dream a reality.” - Walt Disney
Even though the parks will be crowded, Everest probably won't be that crowded... it's not really being promoted as being open. And chances are it won't be open everyday that weekend anyway. It's very hit or miss.