What do you want to do with them on the external drive?
Are you wanting to 'backup' your iPhoto library? Or to get the raw image files out?
If you're trying to backup, just copy your iPhoto library from your Pictures file to the LaCie drive by dragging and dropping it.
If it's only those files you want, just select them all and drag them onto your LaCie icon (might be best to create a new folder on there so you have something to drag them into)