The UK Border Agency will begin accepting applications for Tier 2 for skilled workers and Tier 5 for temporary workers on 27 November 2008.
If you are in an immigration category (such as the Work Permit scheme) that will be replaced by Tier 2 or Tier 5 and you want to extend your stay in the UK on or after 27 November 2008, you will need to take a look at transitional arrangements for your immigration category.
See here for more details.