Those proxies are IRC Proxies.
I think you cannot download through them, download is using your connection.
I think mIRC is rather made for chatting, but you can changing files with a ctcp protocol: dcc (send/get) with other chatterz or you can made a fileserver where people can connect to download.
But I have no idea for using a proxy as you have for download with mIRC...
Anybody else?
Sarkanyka
irc@lap.hu