Most companies require you to get yourself to Anchorage or Fairbanks at your own expense. From ANC or FAI, your company will provide roundtrip flight service to the slope at no cost to you.
Shared Services Aviation, a charter flight service jointly owned by ConocoPhillips & BP, conducts most of the flights. They operate Boeing 737s but will be switching to a different jet aircraft in 2009/2010. You can see their daily flight schedule here: North Slope Flight Schedule.