How to validate xml with undefined elements and attributesl

Can anyone please suggest the correct way to ensure that a valid xml document may be correctly validated by a schema that does not contain all the elements or attributes that are included in the xml.
The reason for this is for development purposes - new elements are being added for prototyping and do not require validation, but the original data does necessitate validation.
I have tried using the any element but MSXML4 produces an error as it is unable to interpet the any as belonging to anthing other than those elements I have already declared.
e.g.
<complexType>
<sequence>
<element name="aaaa" minOccurs="0" maxOccurs=unbounded"/>
<element name="bbbb" minOccurs="0" maxOccurs=unbounded"/>
<any namespace="##any" minOccurs="0" maxOccurs=unbounded"/>
</sequence>
</complexType>

Thanks

Neil