The Ibook
-I have used the 12" powerbook and the 800MHz Ibook and they feel the
same IMO(with 640MB RAM).
-You will have to do the
hack on the Ibook to enable monitor spanning.
Photoshop
- For me it runs fine on an 800Mhz Ibook. I do web design and photoshop
image retouching and on 50MB files it works fine.
- If you are doing big files (over 50MB) the machine will be slow, better get a 15 inch
- If you are doing only basic retouching ( image cropping, Levels, actions etc) it will be ok.
Anything more complex you will need the second screen and it will be slow.