small problem with the XML - XSD relationship

In the XML below there is an error in the first 5 lines. I have tried everything and still it will not read the XSD file which i need to validate along with the dt:dt= restriction. If someone has an idea of what I have done wrong can you let me know. Thanking in advance.

<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="list1.xsl"?>
<!-- James Walton, Asssignment 2 -->
<listing
xmlns:dt="urn:schemas-microsoft-com:datatypes"
xsi:noNamespaceSchemaLocation="list1.xsd">

<property region="CEN">
<type>T</type>
<add>Green Park</add>
<town>Strode</town>
<gar>N</gar>
<bed>2</bed>
<sole>N</sole>
<dreg dt:dt="date">5-Sept-97</dreg>
<sold>N</sold>
<price dt:dt="number">£44,950.00</price>
</property>
</listing>

Just in addition to the above. This is the error that I get on screen:

Reference to undeclared namespace prefix: 'xsi'. Line 6, Position 44

xsi:noNamespaceSchemaLocation="list1.xsd">