Xsl Transformation, XML - saving data to file

Hi.

I am trying to build simple web application in ASP.NET.
I have xml file with data and xsl file to transform xml file into html document which will be presented in the browser window.
What funcionallity do I want?
I want user to enter some text into textboxes and I want this data to be saved into source xml file by clicking for example Save button - I think that it is inversion of transformation process (from html into xml). Can I do something like that? Is it hard to achieve?

regards