Here is an example of how such a decorator might look like:
<#include "/includes/decorators/header.dec">
    <h2>${title}</h2>
    ${head}
    <img src="${base}/images/logo.gif" border="0">
    <td valign="top" class="body">
        <div class="header">
            <span class="pagetitle">${title}</span>
        </div>
        ${body}
    </td>
<#include "/includes/decorators/footer.dec">
        [web-app]/WEB-INF/lib. 
        	The SiteMesh distribution comes with freemarker.jar v2.3rc3[web-app]/WEB-INF/web.xml
        	within the <web-app> tag:
<servlet>
    <servlet-name>sitemesh-freemarker</servlet-name>
    <servlet-class>com.opensymphony.module.sitemesh.freemarker.FreemarkerDecoratorServlet</servlet-class>
	<init-param>
		<param-name>TemplatePath</param-name>
		<param-value>/</param-value>
	</init-param>
	<init-param>
		<param-name>default_encoding</param-name>
		<param-value>ISO-8859-1</param-value>
	</init-param>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>sitemesh-freemarker</servlet-name>
    <url-pattern>*.dec</url-pattern>
</servlet-mapping>
		decorators.xml to reference a .dec file.
<#include "/includes/decorators/header.dec">
    <h2>${title}</h2>
    ${head}
    <img src="${base}/images/logo.gif" border="0">
    <td valign="top" class="body">
        <div class="header">
            <span class="pagetitle">${title}</span>
        </div>
        ${body}
    </td>
<#include "/includes/decorators/footer.dec">
		
	FreemarkerDecoratorServlet puts some things into the context object that you should be aware of:
${Session["user"]}
			<#assign ww=JspTaglibs["/WEB-INF/webwork.tld"]>
<#assign ww=JspTaglibs["/WEB-INF/webwork.tld"]> ... <@ww.property value="myVar"/>
| base | request.getContextPath() | 
| title | Parsed page title (<title>...<title>) | 
| head | Parsed page head | 
| body | Parsed page body | 
| page | SiteMesh's internal Page object |