Programatically download file from document library.

You probably have this kind of scenario, you have developed a document library system base on the WSS object model, users of this system need to download files from backend WSS site, but sometimes these users can't access the backend WSS site, you just grant the proper permission to them in your system, I mean they are probably the reader to your system, but not the reader to backend WSS site. So if they want to download files, you can't just give them a specific URL(eg. You probably have this kind of scenario, you ha