I have a very mixed envirement:
My brother uses Windows and is clearly "not a power user ;) He wants to move large files (ISO CD images etc) from his home broadband network behind a unknown brand of nat router to my Linux box with a Nat router.
1) Large files through two nat routers
2) Semi secured, I want people to have to work at least a little bit to know what we are sending
3) FTP as I understand has a bit of a problem with Nat routers. Also this may be a bit complicated for my brother (active vs passive ftp)
4) Microsoft to Linux
5) Some kind of control on who get the file (password ?). I do not want just anyone to attach to my server and spend days pulling down files