My current solution:
I transfer files from an FTP server I have setup on a Win2K3 server (Port 21). I have a .NET 2.0 Windows Form application (call it MyClientApp) that runs on the client PC that communicates with my FTP server to determine if it needs to get a file. MyClientApp when installs registers itself with the Windows firewall and the ports it uses -- this works in about 70% of the cases. But some clients run Norton or McAfee or other 3rd party software firewalls that block MyClientApp.
This generates a lot of support calls, so I was wondering if there is some other method I can use to transfer files that isn't automatically blocked by most firewall software. I know Port 80 is always left open so that the browser works -- is there a way using .NET 2.0 framework (VB.NET) to reliably transfer files over this port?