Here's a solution for you: Try out "Shareaza" as a free file sharing tool. If you like to share a certain file with someone you can send this certain person a so called "magnet"-url via email. Then the other one fills this "magnet" in (menu-bar "Extras" and then "Download URL") This "magnet" then finds his way to the owner of the file as long as he is online and has opened "Shareaza" and the download via "Shareaza" can start.
If you have questions about using it- just tell me.
Good luck, Stefan
