How to upload a file to a file system in InfoPath form?

IXMLDOMNode hyperlink = thisXDocument.Dom.SelectSingleNode(xpath of textbox control, used as the datasource for the hyperlink);

//you should have a kind of ID for each new request so that the subfolders you create are always unique and there is no possibility to overwrite an existing one
IXMLDOMNode ID = thisXDocument.Dom.SelectSingleNode(xpath to ID);

//top folder under which you can create new subfolders for each request, keep in mind that the users will need read and write permission to this folder !
string strDirectory = @"absolute pathHere_I_Put_My_Attachments_Folder";

//create a new folder
System.IO.DirectoryInfo dir = System.IO.Directory.CreateDirectory(strDirectory + ID.text); 

//write the full path of the new folder into the textbox control you want to use as the datasource for your hperlink
hyperlink.text = dir.FullName;

You can use this code in a button event for example. When everything works create a Hyperlink and use the textbox as the source for the link. Like this the link points to the folder you just created. When people click the link the folder opens and they can just drag and drop all required files into the folder. You can have the link in all views of your process so that the files are available during the entire instance.

Hope this helps