yes, I did it !!!
you can easily create a new library folder with your iPhoto:
1. quit iPhoto
2. rename your actual "iPhoto Library" - for example to "all pictures"
3. open iPhoto again and klick the button for a new library with another name. That creates a new folder which is then your actual iPhoto library.
4. switch to the Finder and choose the library "all pictures" where all your photos are stored in different subfolders depending on their date.
5. pick some photos and drag/drop them onto your iPhoto application -> these photos will be added imediately to your new library.
6. because you ADD these photos to the new library you'll have doubles on your computer, so remember to delete the copied ones from the old library.
7. add as much photos as you need from your old library to the new one till it reaches the size you want.
With that I created different folders for different kinds of photos. To switch beween the different libraries you can use the "iPhoto Library Manager" or just rename the last used library folder, start iPhoto and klick "find library" (costs nothing :-)
I hope I could help you !!!
P.S. If anything is not clear, tell me on my website -> www.havse.de (guestbook) then I'll answer soon :-)