Can I make a substructure to organize my photos?
By "maps" do you mean 'Folders'?
If you want to duplicate your Folder Tree in iPhoto:
Start at the bottom of the hierarchy and drag a folder of images to the Album Heading in iPhoto. The pics will be imported and an Album of the same name created.
You can then create the Enclosing Folders in the iPhoto Window (File -> New Folder) and drag the Album to it. Folders can contain other Folders (Nested Folders) and Albums.
However, is your folder system date based? Then this form of organisation is a bit pointless in iPhoto when Smart Albums or the Calendar tool (Click on the wee magnifying glass in the Search Box) mean you can find the photos taken on any day, month or year at a click. With Smart Albums it's easy to find photos from specific range - say, June 3 to August 25, 2009 etc.
If your folder system is theme based - Xmas pics, Birthday pics etc, then you'll find Keywords are much more flexible, and can be used in conjunction with other criteria for making Smart Albums and searches.