Aperture file import
To add to the previous poster, if you want to poke around inside your Aperture library, right click on it (or control-click) and select "show package contents." What you'll see is Aperture folders represented by regular Finder folders and projects, albums, web projects and smart albums represented by what appear to be files. The projects are actually more packages and you can do the same right click, show package contents and see what's in them. Actual photos are stored each in their own folder with their name all contained in a folder named by the time and date of import.
Be careful about removing (or adding) things directly like this as it won't update Aperture's database (Aperture is fairly smart about synchronizing it's database to the reality on disk, but why take chances?). Copying is safe though.