Rankings - how do they change?

This season hasn't even started, and there's already an interesting topic for debate:  Rankings.

The preseason rankings are already in, and Ohio State was expected to play with Braxton Miller as their starting QB.  As a result, they were ranked very highly in the polls, in the 5-6 range.

Now that Miller is out for the season with an injury, opinions of Ohio State are reasonably different.  If the rankings were redone, Ohio State would not quite get such a high ranking.

So how is this going to play out over the course of the season?  I'm sure that by midseason, the ranking will even out.  Either Ohio State will win most or all of their games, justifying a high ranking, or they'll lose a few and drop accordingly.

But what about after week 1?  If Ohio State beats Navy, will they stay in their 5-6 spot (assuming all of the teams ahead of them also win in week 1) or could they possibly drop a few spots to better reflect voters' opinions of the team?

The preseason rankings are huge in the outcome of the season, since a large reason for movement in the polls is simply attrition by losing.  Most teams in the middle of the top 25 usually need the teams above them to lose in order to move upward in the polls.

It should be interesting to see how this shakes out.