If you create a local iDisk on your MacBook Air that is connected to your MobileMe account, and then go to System Preferences > MobileMe > iDisk and click Start in the Syncing section of the pane, that should suit your needs.
If you find iDisk synchronisation too inflexible via iPad, you might want to take a look at Dropbox, which is iPad/iPhone/ Windows/Mac compatible.
In terms of creating a local iDisk on an iPad 2, as the iPad is fairly locked down in terms of file storage (outside of iTunes syncing and apps, and the iWork file area), there’s no local iDisk option here.
The iDisk application for the iPad only allows you to view and share files in your iDisk.






