As Lightroom is your primary Photo Manager then the easiest way to do it is to use something that will send your pics from LR to iPhoto: this
http://www.suffix.be/blog/lightroom-iphoto-export
had a plug-in for LR to do the job. It hasn't been updated in a while, so I'm not sure if it will work with later versions LR.
The problem using LR and iPhoto is that iPhoto cannot read the LR library. So, while you can import the Original files to iPhoto you'll not get any of the edits or processing that you've done on them in LR. To get that you'll need to export from LR and then import to iPhoto.
Other than that: A Referenced Library will import pics without copying them to the Library:
*How to do it:*
Simply go to iPhoto Menu -> Preferences -> Advanced and uncheck 'Copy Files to the iPhoto Library on Import'.
*What Happens:*
Now iPhoto will not copy the files, but rather simply reference them on your HD. To do this it will create an alias in the Originals Folder that points to your file. It will still create a thumbnail and, if you modify the pics, a Modified version within the iPhoto Library Folder.
*Some things to consider:*
1. Importing and deleting pics are more complex procedures. You have to to put the files where they will be stored before importing them. When you delete them you'll need to remove the files from the HD yourself.
2. You cannot move or rename the files on your system or iPhoto will lose track of them on systems prior to 10.5 and iPhoto 08. Even with the later versions issues can still arise if you move the referenced files to new volumes or between volumes.
3. Most importantly, migrating to a new disk or computer can be much more complex.
4. Because iPhoto has no tools for managing Referenced Files, if, for some reason, the path to the photos changes then you could find yourself resolving aliases for +each photo in the Library+ one by one.
My own opinion:
I've yet to see a good reason to run iPhoto in referenced mode unless you're using two photo organiser
If disk space is an issue, you can run an entire iPhoto Library from an external disk:
1. Quit iPhoto
2. Copy the iPhoto Library as an entity from your Pictures Folder to the External Disk.
3. Hold down the option (or alt) key while launching iPhoto. From the resulting menu select 'Choose Library' and navigate to the new location. From that point on this will be the default location of your library.
4. Test the library and when you're sure all is well, trash the one on your internal HD to free up space.
If you're concerned about accessing the files, There are many, many ways to access your files in iPhoto:
*For Users of 10.5 and later*
You can use any Open / Attach / Browse dialogue. On the left there's a Media heading, your pics can be accessed there. Command-Click for selecting multiple pics.
You can access the Library from the New Message Window in Mail:
*For users of 10.4 and later* ...
Many internet sites such as Flickr and SmugMug have plug-ins for accessing the iPhoto Library. If the site you want to use doesn’t then some, one or any of these will also work:
To upload to a site that does not have an iPhoto Export Plug-in the recommended way is to Select the Pic in the iPhoto Window and go File -> Export and export the pic to the desktop, then upload from there. After the upload you can trash the pic on the desktop. It's only a copy and your original is safe in iPhoto.
This is also true for emailing with Web-based services. However, if you're using Gmail you can use
iPhoto2GMail
If you use Apple's Mail, Entourage, AOL or Eudora you can email from within iPhoto.
If you use a Cocoa-based Browser such as Safari, you can drag the pics from the iPhoto Window to the Attach window in the browser.
*If you want to access the files with iPhoto not running*:
For users of 10.6 and later:
You can download a free Services component from
MacOSXAutomation which will give you access to the iPhoto Library from your Services Menu. Using the Services Preference Pane you can even create a keyboard shortcut for it.
For Users of 10.4 and later:
Create a Media Browser using Automator (takes about 10 seconds) or use this free utility
Karelia iMedia Browser
Other options include:
1. *Drag and Drop*: Drag a photo from the iPhoto Window to the desktop, there iPhoto will make a full-sized copy of the pic.
2. *File -> Export*: Select the files in the iPhoto Window and go File -> Export. The dialogue will give you various options, including altering the format, naming the files and changing the size. Again, producing a copy.
3. *Show File*: Right- (or Control-) Click on a pic and in the resulting dialogue choose 'Show File'. A Finder window will pop open with the file already selected.
Regards
TD