The following was posted on Foxsports.com by regular Kevin Hench (original article, published 12/5/06, can be found  here):

To derive a team's poll percentages in the Harris Interactive and USA Today polls, each team's point total is divided by a maximum 2825 possible points in the Harris Interactive Poll and 1550 possible points in the USA Today Poll. Teams are assigned an inverse point total (25 for No. 1, 24 for No. 2, etc.) for each of their respective computer poll rankings to determine the overall computer component. The highest and lowest ranking for each team is dropped, and the sum total of the remaining four rankings is divided by 100 (the maximum possible points). This figure produces a Computer Rankings Percentage. The six computer ranking providers are Anderson & Hester, Richard Billingsley, Colley Matrix, Kenneth Massey, Jeff Sagarin and Peter Wolfe. Each computer ranking accounts for schedule strength within its formula. The BCS Average is calculated by averaging the percent totals of the Harris Interactive and USA Today Polls, and Computer rankings. The highest BCS Average receives the No. 1 ranking, the second highest receives No. 2, and so forth.