Copy a document to stand alone web server with a username and password

My application needs to copy a .pdf doc to our web server.  It works fine when done from my pc because I am also the webmaster and so have permissions on this server not part of our network.  However, I am creating a VB.NET windows application  that requires the users to be able to upload or delete a .pdf documents in a folder on the web server.  We can give them each their own permissions to that folder but my network administator would prefer one special username and password be used instead.  We have created the special username and pw but I do not know how to code my app to use the special username and pw instead of the users windows username and pw.  Can someone help with this?  I have been searching the net but so far cannot find anything that helps.  Maybe my search is not stating it right, whatever the reason I have not been able to find what I need.  I sure could use some help.  Thanks in advance.