If you want a simple way to tag your images you should checkout my Geotagger (http://craig.stanton.net.nz/software/Geotagger.html). Drop your images onto it and it'll grab the location that Google Earth (V4 only) is looking at. It does work with photos that are in iPhoto, but iPhoto doesn't notice the changes (it must have that stuff cached somewhere), so I recommend tagging your pictures before adding them to iPhoto.