SqueakFS exists, and is able to make an image available to the outside (file system) world. We're in the process of setting up a development repository (based on SVN, mind you). In the meantime, it's available from www.squeaksource.com/SqueakFS.html in the current version.
Ah good. I must have run across it at some point and forgotten about it.
There is also the FTP server that I wrote together with Ian at ESUG 2005.
http://www.cincomsmalltalk.com/userblogs/avi/blogView?showComments=true&...
I used it for a while to develop from within an external editor, but in the end the clumsy Squeak environment is still less annoying than an external editor.
Lukas