BigSam,
Samples are provided (at the bottom) of the article.
Here is your specific one.
print 'Filter on specific Countries and OrderDate'
EXEC uspOrderDetailsGetByXmlParams '
<ParametersDS>
<CustomerCountry>
<CountryName>USA</CountryName>
</CustomerCountry>
<SingleValueParam>
<OrderDateAfter>1/1/2006</OrderDateAfter>
</SingleValueParam>
</ParametersDS>
'