VF to excel

<apex:page standardController="Opportunity" showHeader="false" contenttype="application/vnd.ms-excel#SalesPacket.xls" >

    <apex:dataTable value="{! Opportunity}" var="opportunity" >
        <apex:column headerValue="Opp Name" value="{! opportunity.name}" />
        <apex:column headerValue="Owner Name" value="{! opportunity.owner.name}" />
        <apex:column headerValue="Account Name" value="{! opportunity.account.name}" />
        <apex:column headerValue="Billing Address" value="{! opportunity.account.billingstreet}" />

    </apex:dataTable>
    <apex:dataTable value="{!opportunity.OpportunityContactRoles}" var="OC">
                <apex:column headerValue="Contact Name" value="{!OC.Contact.Name}"/>

                <apex:column headerValue="Contact Role" value="{!OC.Role}"/>

     </apex:dataTable>

</apex:page>