Here is some quick Applescript that uses ExifTool to write Copyright, Title, Comments, and Keyword exif data to selected photos in iPhoto:

This script is released under the Creative Commons.

-- This applescript will set the exif keywords, name,

--  and comments of all selected iPhoto images using

--  the information current in iPhoto.

--

-- Author: Andrew Turner (http://highearthorbit.com)

--

property copyright : ¬

		"Copyright Andrew Turner, 2005. All Rights Reserved."

property URL : "http://highearthorbit.com"

property exifToolOriginal : "_original"

-- True retains copyright, False means Public Domain

property Copyrighted : "True"
tell application "iPhoto"

	activate

	try

		copy (my selected_images()) to these_images

		if these_images is false or (the count of these_images) ¬

			is 0 then ¬

			error "Please select a single image."
		repeat with i from 1 to the count of these_images

			set the keywordslist to ""

			set this_photo to item i of these_images

			tell this_photo

				set the image_file to the image path

				set the image_title to the title

				set the image_filename to the image filename

				set the image_comment to the comment

				set the assigned_keywords to the name of keywords

			end tell

			repeat with j from 1 to the count of assigned_keywords

				set the keywordslist to keywordslist & " -keywords+=" ¬

					& item j of assigned_keywords

			end repeat

			set output to do shell script ¬

				"exiftool -title='" & image_title & ¬

				"' " & keywordslist & ¬

				" " & " -comment='" & image_comment & ¬

				"' " & " -Copyright='" & copyright & ¬

				"' " & " -CopyrightNotice='" & copyright & ¬

				"' " & " -Rights='" & copyright & ¬

				"' " & " -Marked='" & Copyrighted & ¬

				"' " & "'" & image_file & "'"

			do shell script "rm '" & image_file & "'" ¬

				& exifToolOriginal

		end repeat
		display dialog "Exif writing complete."

	on error error_message number error_number

		if the error_number is not -128 then

			display dialog error_message buttons {"Cancel"} ¬

				default button 1

		end if

	end try

end tell
on selected_images()

	tell application "iPhoto"

		try

			-- get selection

			set these_items to the selection

			-- check for single album selected

			if the class of item 1 of these_items is album then error

			-- return the list of selected photos

			return these_items

		on error

			return false

		end try

	end tell

end selected_images

You can grab this script and a simpler Copyright only, as well as a Location (latitude/longitude/city,region,country) script here.