The Voter News Service is an organization formed by a consortium of the top news networks and agencies: ABC, CBS, CNN, NBC, Fox, and the Associated Press. It's purpose is to gather information, primarily through exit polling, about elections. It predicts which candidate will win a given race. Contrary to popular belief, the networks don't compete for coverage, they pool their resources.
Though a horrible failure during the last Presidential election, the VNS, as it's commonly called, has been extremely accurate in the past. They usually do accurately predict the outcomes of the various races they cover. However, to avoid another catastrophe with the VNS calling the wrong winner, the consortium has added new safeguards for the 2002 midterm election. First, as always the Associated Press (AP) will also run an independant prediction system that will serve as a double check for the VNS. However, this time several networks, including CNN, will also have their own teams perform their own exit polling. In addition, the AP will now be making its exit polling information available to the entire consortium. The result of these and other safeguards will be that, hopefully, the VNS will be more accurate. The downside is that close races will be called later than the during the last Presidential election.
Thanks to CNN for the information on the VNS.