distributable databbase app

hi,

i am new to database and ADO.net apps, but as far as i know there must be a database engine or data provider that the app uses to access data in a database, eg SQL server, OLE DB and stuff like this, and the machine which is going to use this database app must have the runtime files of the data provider the app uses.

so i want to know which data provider should i use to target more users, i need one whose runtime files is installed by default in windows, or which has a small sized, free runtime files that i can distribute with my app.

Thanks