C# DB in client side [on hold]

I work with C # WinForm, i want to manage a DataBase in Client side which should be supported the Version 2.0.

i want a good advice about how to manage db in client side . From my experience customers have support problems even to "access" (office) so i need something more simple.

Is there an advanced DB except XML sheets? If not, would it be a good idea to save everything on the server side (by WebService)? I need to send back and forth a list of thousands...