What are you planning to achieve???
If you intend to store XML as a zipped BLOB, you cannot access it as XML. You will have to extract the data as a bitstream using an application, unzip and parse it ...
If you store the XML as XML type data in V9, you will be able to exploit the new functionality to manipulate XML data ... But it is likely to take more disk space and maintanence ...
I don't think there will be a document about storing XML data as blob
HTH
sathyaram