Trying to mess around with the Enterprise API and I can't seem to get my XML request setup correctly.

Here is my XML update request:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:urn="urn:enterprise.soap.sforce.com" xmlns:urn1="urn:sobject.enterprise.soap.sforce.com">
      <soapenv:Header>
            <urn:SessionHeader>
                  <urn:sessionId>tricks</urn:sessionId>
            </urn:SessionHeader>
      </soapenv:Header>
      <soapenv:Body>
            <urn:update>
                  <urn:sObjects xsi:type="urn1:Account">
                        <urn1:Id>0015000000Lij8E</urn1:Id>
                        <Name>test</Name>
                  </urn:sObjects>
            </urn:update>
      </soapenv:Body>
</soapenv:Envelope>

And here is the response:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
   <soapenv:Body>
      <soapenv:Fault>
         <faultcode>soapenv:Client</faultcode>
         <faultstring>The prefix "xsi" for attribute "xsi:type" associated with an element type "urn:sObjects" is not bound.</faultstring>
      </soapenv:Fault>
   </soapenv:Body>
</soapenv:Envelope>

What am I messing up? I was using this as a guideline but it is very old and may be outdated: http://wiki.developerforce.com/index.php/Enterprise_Update

Thanks,

Jason