Both library are in your home folder.
Look in the Photos folder for "iPhoto Library" -- it's a single file, but actually contains all of your iPhoto photos + data.
Look in the Music folder for a folder called "iTunes Library".
If you drag either of those folders up to your iDisk folder, it should make a copy of them.
You might also google "mobileme backup". There is an Apple tool out there that will backup your home folder (or just certain files) automatically for you (to your iDisk).