How can I indicate to users that my IIS website is undergoing maintenance?

For my IIS website, I'd like to redirect ALL requests to ONE page. The purpose of this is that I want to do some maintenance on the database (take it off-line) that all my web applications use. I have about 50 web apps running under this website, so I'd like to avoid visiting each of them to change something. I'm thinking I could make a single change in machine.config? Any hints would be appreciated.

If you are using ASP.NET 2.0 (or higher), you can drop an app_offline.htm page on the root.

More info here.

in webconfig

 <rewrite>
        <rules>
            <rule name="redirect all requests" stopProcessing="true">
                <match url="^(.*)$" ignoreCase="false" />
                <conditions logicalGrouping="MatchAll">
                    <add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true" pattern="" ignoreCase="false" />
                </conditions>
                <action type="Rewrite" url="index.php" appendQueryString="true" />
            </rule>
        </rules>
    </rewrite>