Earlier versions of Apple's iPhoto stored its library information in a regular folder structure. Around version 7 Apple changed that approach and iPhoto began hiding its folder structure inside a package file. While this makes the applications presence on the drive neater and theoretically more portable, it does hide the images in iPhoto's library from Lightroom.
If you want to migrate your iPhoto library to Lightroom I have some good news and some bad news. The good news is that it is relatively easy to import the files. The bad news? Your edits will not migrate easily. Unlike Lightroom, files that you edit in iPhoto are saved as a separate file. You can import these edited files but you will have both an original and the edit without any connection between them. Essentially, you wind up with two separate images. If you're still game here is how you do it.
Locate your iPhoto Library package. It's is in the Pictures folder by default.
Right click (or Control click) on the iPhoto Library and choose Show Package Contents.
A new Finder window will open revealing the folder structure hiding inside the package.
Lightroom cannot see inside this package so we need to make an alias to the Originals folder. This is where your original image files are stored. Right click (or Control click) on the Originals folder and choose Make Alias.
This creates the alias at the same folder level as the Originals folder.
Lightroom won't be able to see this either so we need to drag the alias to a regular folder. The desktop is a convenient place since we won't need the alias once we're done.
Now open Lightroom and click Import in the Library Module.
Choose the Originals alias from the desktop (or wherever you chose to save it).
In the import dialog it is important to choose the option to Copy photos to a new location and add to catalog. You can't leave them at their original location because Lightroom won't be able to get to them inside the iPhoto Library package. Choosing to move the files will damage the iPhoto Library package and you won't be able to open the library in iPhoto. So Copy is the best choice here.
When the import is finished you have your iPhoto images in Lightroom!
If you choose to also import the edited version just follow the same make an alias procedure for the Modified folder inside the iPhoto package. Once you're done you can delete the alias files.
Keep in mind that many things may also be left behind. iPhoto will store EXIF and keywording in expected locations. However, IPTC data may not migrate with your files.