Well, in ASP.NET server side code has access on server machine. They don't have any control on client system - so you cannot use C# server code for the same even if the path is configured.
What is left with you is to use
ActiveX file object in Javascript to access client system and files.
To start with, have a look at these:
File access via Jsavascript[
^]
Link 2[
^]
Link 3[
^]
Google for more, if needed.