c# routines to read/write XML files

I would like a c# class file and a simple example application to: * C# class (separate class file which can be called from various forms in application) with simple example application to demonstrate usage * Encrypt [login to view URL] and [login to view URL] files <!-- --> * Class to read settings from [login to view URL] file into public variables (at application start up) to be used throughout system * Class to write settings to xml files from textboxes on form * Class to update existing variables in memory with new xml settings * Class to read provider names in [login to view URL] (ie, voipfone; interfax) and populate a combo box * On click of button on form, read settings from appropriate section in [login to view URL] (ie, interfax) when textbox equals (ie, "interfax") and store settings from xml into public variables * Class to add an attribute (ie, "newsetting") to [login to view URL] to existing element * Class to read <usersetting1> and <usersetting2> to variables on button click on form see attached for xml files.