Using schema in files

All schema examples everywhere I look point to the W3C site 
for the definition of the schema language e.g. 

 <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

That's fine for people who can be guaranteed to be online to the 
internet but I want to download the schema definition into a local 
file so it's always accessible to my customers e.g.

<xs:schema xmlns:xs="c:\myapp\XMLSchema" >
<xs:schema xmlns:xs="c:\myapp\XMLSchema.xsd" >
<xs:schema xmlns:xs="file://c:\myapp\XMLSchema" >
<xs:schema xmlns:xs="file://c:\myapp\XMLSchema.xsd" >
<xs:schema xmlns:xs="file:///c:\myapp\XMLSchema" >
<xs:schema xmlns:xs="file:///c:\myapp\XMLSchema.xsd" >

Am I, in theory allowed to use a file? Are _any_ of the above
correct forms?

I've tried all different types of syntax to use a filename but the Microsoft 
XML parser 4.0 preview July 2001 always chokes. The error happens 
when I use XMLSchemaCache40's add method on a schema file that tries 
to refer to a file in the xmlns attribute using, for example, any or the above. 
No problem occurs when I use the original http method.

Any clues anybody? Has anybody managed to use a schema 
in a local files rather than a website? With the Microsoft 
component? What files should be downloaded to use the W3C schema 
definition?

Gaz Robertson