win application data storage options

I am developing a windows application with C# in which user adds data into tables. User can customize these tables depending upon his requirement. For storing and querying this data what options should i consider?? As the data tables are un-predictable[as user can customize them] mapping them to DB table appears difficult. So I am thinking about XML files for storing the data, am i going in the right direction?? Other requirements are

1. The data should be located on a centralized server


2. access to the data should be controlled.


3. The targeted end users should not be troubled with DB configuration and related issues.

I have gone through other posts but none of them could make my mind clear.

thanks indra