(Didn't you ask this before?)
Have you tried Kasyan's http example, listed somewhere last month? Instead of sending http commands ('get', 'post') you should send ftp commands, but that ought not be a problem.
Ed. OK, I found it: Is it possible to load web content?
Searching this forum alone for 'socket' gave tons of other useful results.
Bridge CS3 SDK has a sample script: BasicFTP.jsx. So it should be possible to connect to FTP server from InDesign via Bridge application over BridgeTalk. I can't test it myself since don't have access to any FTP server.