Its actually pretty easy. If you follow directions well, move slowly and
don't try to force anything, you should have no problems replacing your
hard drive. As you are following the instructions, make sure you tape
the small parts onto sheets of paper with part sizes and step numbers
written on them.
I've replaced drives in 4 or 5 powerbooks. The 12" ones are by far the
toughest. Lots more parts to take out.
In addition to putting a 160GB drive in my 15" powerbook, I replaced the
optical drive with one of
these. It went very smoothly, and works perfectly.
The only problem I've had is that Apple's DVD Player application doesn't
seem to want to recognize DVDs in my now external superdrive. Other
players, like VLC work fine with the external superdrive.
I now have a >300GB powerbook!