validating instance against schema? (my first post to the list-:))

Hi,
I want to validate my xml instance against the schema.
i want to do this programatically.
now one way i know of is to set the schema attribute in the document and apply a parser with validation set to true.
now my problem:
there may be 1000 instance documents of that schema which may be changing frequently in memory.
everytime if i validate using the above method, will the parser load the schema xsd from the file system? i think it will. and if it does, then the performance hit would be unacceptable. 
isnt there a way in which all the "schema objects" can be created in memory once and used again and again for validating its corresponding instance documents? 

something like a validate(oDocument:Document, oSchema:Schema):ValidationErrors api somewhere? 

Thanks in advance,
Amol