XML transformation library

Question

Hi, I´m searching for a library - free or commercial - which gives me the possibility to transform files (e.g. ini, csv, ...) to XML by the use of schema files. My aim is to develop a program in c# which has to transform XML data to csv, ini, ... files and vice versa. I think .NET gives me a good possibility to transform XML to what ever using XSL, but what about the way back. Therefore Iám searching for a library giving me that possibility. As the source files which have to be transformed have different structure/look the use of schema files are a must. Anybody knows a good product? Thanks in advance Andreas