Looking for an example of importing an xsd into a wsdl

I'm looking for an example of importing an xsd schema into a wsdl. My
current attempt is failing WS-I validation with a namespace error. This is
my first attempt to import an xsd so I may be making a basic syntax error
somewhere. Can anyone point out what is probably a really basic error?
Here's what I'm doing:

xsd file:

<?xml version="1.0" encoding="windows-1252" ?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
            xmlns="http://www.example.org"
            targetNamespace="http://www.example.org"
            elementFormDefault="qualified">
  <xsd:complexType name="sigRequestMessage">
    <xsd:sequence>
      <xsd:element name="publicKey" type="string"/>
      <xsd:element name="privateKey" type="string"/>
    </xsd:sequence>
  </xsd:complexType>
  <xsd:complexType name="complexType1">
    <xsd:sequence>
      <xsd:element name="Signature" type="string"/>
      <xsd:element name="expiration" type="timeDate"/>
    </xsd:sequence>
  </xsd:complexType>
</xsd:schema>

import section of wsdl:

  <types>
    <xsd:schema>
      <xsd:import id="Messages.xsd"
                  schemaLocation="../../XSDDocument/Messages.xsd"
                  namespace="messages"/>
    </xsd:schema>
  </types>
  <message name="ReturnSignature">
    <part name="SigAndExp" type="messages:SigReplyMessage"/>
  </message>
  <message name="RequestSignature">
    <part name="Keys" type="messages:SigRequestMessage"/>
  </message>

The WS-I test failes with a message:

Unable to determine namespace of 'messages:SigReplyMessage'

Thanks,
Bret