<p>Is there any way to Write files to App_Data under medium trust hack?</p>

<p>Im sure I've heard about some hack, is that true?</p>

I don't think you are able to create new files, but you should be able to write to existing files in the App_Data folder.  But I have honestly never experienced any problems with Medium Trust and writing to the App_Data folder.  Are you sure it has the necessary permissions needed for writing files to the hard drive?