U need to set up a server software on teh PC u want to download from. If your IP is dynamic get a no-ip.info DNS account. If it is shared on the network and you do not have access to the router - you are out of luck.
If you have your own IP - you are good to go! Set up that server and get a ftp client software [cute FTP, flash FXP]. then you need to set up your connection on the client so it will run in PASSIVE if default mode does not work. Try using port 21 for your server. If you can't then you will not be able to connect to your server from computers that are on a shared internet connection.
Any other questions - pm or reply. I can really help - been running an FTP for a couple of years now - different ISPs, different networks.
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