Only if...
Only if you have "local iDisk" turned on. If you do, you can view/edit files of most any kind with or without an internet connection that are in your iDisk. Once you do have an internet connection your iDisk will sync and both copies (locally on your Mac and on your iDisk) will be the same. If you do not have your local iDisk turned on and you do not have an internet connection you can not see or use your on-line iDisk...
You turn your local iDisk on in system pref's / MobileMe / iDisk / iDisk "sync" on / or off.