Setting the Timeout Period on a Site

 VWD 2008 Express.  IIS 6.0.  Forms Authentication.
My web site uses forms authentication (in case that makes a difference).  Folks who are using the site indicate that it is timing out on them (logging them out) before they can finish some entries.  How can I increase the timeout period?  The following is my web.config file in my root directory:
<?xml version="1.0"?> <configuration> <configSections> <sectionGroup name="system.web.extensions" type="System.Web.Configuration.SystemWebExtensionsSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"> <sectionGroup name="scripting" type="System.Web.Configuration.ScriptingSectionGroup, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKey ...