well no one is answering you so i thought id take a shot at this, but please bear in mind ive never tried this so i could be horribly horribly wrong.
that little disclaimer out of the way ive noticed that when you connect to your iDisk there is a folder titled "Sites" that contains the .html files created when i used apples guided site creation. I am assuming that if one would drop their own .html files into that folder one could make their own custom website. Just title your first page index.html and i think you should be set.
o and btw that Goliath app Arn told us all about is a wonderful for connecting to your iDisk in OSX, since iDisk in OSX is usually painfully slow. With Goliath everything is pretty instantaneous.
[edit] whoa ensign i think you beat me to the punch. i just read this in the iDisk read me file
"¥ Sites: HomePage stores your Web pages in this folder. If you create a site using another tool, you can publish the site by copying the files to this folder."