You misunderstand the operation of iPhoto. The images in iPhoto are kept in a Library maintained by iPhoto. The albums are only available within a Library. If you want iPhoto images on your external HD, you need to create a new iPhoto library on that drive. You can do that by holding down the Option key while booting up iPhoto. That will give you the option to create the new library, and that's also how you tell iPhoto which library to use when opening the app.