Help in validation of a Subtree!!

Hi...
  Here is my problem - 

Is it possible to validate a subtree of xml file with some XSD/DTD file? My
requirement is to validate different subtrees of 1 xml file by Different XSD
files?? 
If this is possible, which parser I can use. I am working in c++
environment.

Cud anyone help me in this..I'll really appreciate an urgent reply.

Thnx in advance,
Manoj