You can use the 2005 point CHARTS to calculate the 2006 point cost, but not the calculator. Unless you are going the week before Easter or the week after Easter or around Thanksgiving, you do not need to make any adjustments to the charts. The Easter weeks are always peak season and points for the end of November will vary depending on when Thanksgiving falls.
You can't use the claculator because it depends on the exact date - weekend nights cost more than weekday nights and of course those are different dates from year to year. The charts are easier to use for planning purposes anyway (IMHO) - less work and clicks of the mouse, LOL!
If you need help calculating points for an Easter or Thanksgiving vacation, post your specifics, and we'll be glad to help.
Best wishes-