No it's not possible to do this because the file system (NTFS) laks support for locking sections of files. AFAIK, there isn't a file system on this earth that supports this. It sounds like you're treating an XML file as a small database, when in fact, you need full database support. It looks like in order to implement this requirement, you're going to have to rewrite your data access layer to use a full database, such as SQL Server Express or SQL Server Mobile.
A guide to posting questions on CodeProject[^]
Dave Kreskowiak Microsoft MVP Visual Developer - Visual Basic
2006, 2007