If you open the iPhoto Library package you can
COPY the Originals folder to the desktop and from there to the PC. That folder will have subfolders that represent all of the Events in your Library.
However, if you want the keywords, titles and comments to be embedded in the file they follow Terence's suggestion but with the option to include keywords, titles, etc.
A third option, which will also give the keywords, titles and description embedded in the files is to:1 - follow the first part of
Tutorial #2 and 2 - follow the instructions in Paragraph 1 above.
TIP:
For insurance against the iPhoto database corruption that many users have experienced I recommend making a backup copy of the Library6.iPhoto (iPhoto.Library for iPhoto 5 and earlier) database file and keep it current. If problems crop up where iPhoto suddenly can't see any photos or thinks there are no photos in the library, replacing the working Library6.iPhoto file with the backup will often get the library back. By keeping it current I mean backup after each import and/or any serious editing or work on books, slideshows, calendars, cards, etc. That insures that if a problem pops up and you do need to replace the database file, you'll retain all those efforts. It doesn't take long to make the backup and it's good insurance.
I've created an Automator workflow application (requires Tiger), iPhoto dB File Backup, that will copy the selected Library6.iPhoto file from your iPhoto Library folder to the Pictures folder, replacing any previous version of it. It's compatible with iPhoto 6 and 7 libraries and Tiger and Leopard. iPhoto does not have to be closed to run the application, just idle. You can download it at Toad's Cellar. Be sure to read the Read Me pdf file.
