If you're using OSX 10.3 Panther, the iDisk always appears as a folder on your hard drive. Then when you connect to the internet, it will sync the folder on your drive with the actual, online iDisk and give you access to online features like the Software folder. Perhaps this could be the source of your trouble (trying to access these features offline)?
Also, try Go>iDisk>My iDisk in the menubar to see if it connects properly.