.Mac now has a friendly web-based UI for access to iDisk -- there's an iDisk button on your .Mac account's homepage. But if you'd like to get there more easily (via your own bookmark, for instance), here's the direct URL:
http://idisk.mac.com/your_.Mac_ID/?view=web
Replace your_.Mac_ID with your .Mac username; leave off the "@mac.com" portion. The iDisk interface is invoked via a JavaScrpt link on the iDisk button, and it may not be super obvious that the above is the URL needed. A simple tip, but hopefully one that saves you some time.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060117041800419