How can I pass a large XML document from a column of data type ntext to a stored procedure

I'm trying to "prepare" a large xml document that we've
stored (as a string) in our database as an ntext
document. I can't seem to find a way to pass the ntext
datatype to sp_xml_preparedocument. Ntext are not allowed
as local variables, and I'm not sure how chopping up the
ntext, with readtext can help me.

sp_xml_preparedocument @.idoc output, (ntext)

In SQL 2005, you can cast the ntext to nvarchar(max) or the XML datatype and go from there using either OPENXML or XQuery to manipulate the XML.

For SQL 2000, if you know the offset of the data in the buffer, you can use the READTEXT functions to access them. Otherwise you could write code outside of the database that selected the values and converted them using native or managed data access API's. But in general in SQL 2000 you cannot have a variable that is bigger than 4000 unicode characters. SQL 2005 removes this restriction.