Update db

I have this scenario:
1. XML file with schema and data is created from SQL Server tables. XML file
contains 6 tables, some of them have rows, some of them are empty.
2. XML file is given to the person with Pocket PC.
3. XML file is used to populate DataSet on the Pocket PC.
4. User adds new rows, changes values, deletes some rows.
5. Altered dataset is saved back to XML file.
6. XML file is given back to the person who initially created it.
7. XML file is used to populate DataSet.
8. Data from this Dataset should replace existing data in SQL table (deleted records should be deleted from DB, new should be added, edited should be updated with new values).

How to do this?

I only know the way to update SQL Server tables by going through each record in each table, compare with existing data and make decision what to do.
I was wondering if there is more simple and compact way to bring updated
stuff into SQL Server DB?
Everything is going to be done in VB 2005

Thank you

Vlad