Setting content expiration on IIS 7

See also Mike Knowles post on SharePoint IIS Content Expiration settings.
On IIS Manager, click on the site under the "Sites" folder.
Expand to show the subfolders under the site.
Click to select the subfolder you want to modify.
Go to Features view on the main panel.
Open the "HTTP Response Headers" feature.
Under "Actions" on the right column, click on "Set Common Headers..."
You should see the content expiration settings in the popup ("Set Common HTTP Response Headers") that appears.