Here are the instructions I used for the windchimes, including instructions for taking apart the drives.
http://www.evilmadscientist.com/article.php/WindChimeStory
I didn't bother with the 5 1/4" platters mentioned in the instructions,
since I couldn't find any.  I also tried to use exclusively pink twine
for enhanced eye-catching quality.

You will need special star-shaped screwdriver bits for most of the
screws.  Some of the screws may be too small for the bits typically found in hardware stores,
so I just drilled them out carefully.

Here are pictures of a hard drive being taken apart:
http://www.takeitapart.net/archives/hard-drive/

General steps for taking a drive apart:

1. Remove the top lid to expose the platters, spindle, and read/write arms.  Note that some of these screws will be hidden under paper labels.
2. Remove the circuit board on the bottom to expose screws for the spindle and read/write arms.
3. Remove screws on the top of spindle to free the platters.  These may need to be drilled out, if they're too small for the screwdriver bits.
4. On the bottom side, where the circuit board used to be, remove any visible screws for the spindle and read/write arms.  This should loosen them, so the platters can fall out.

There are 2 parts of the hard drive to be careful with:

1. White paper pouch sitting in a slot one of the corners of the hard drive.  This is a moisture-absorbing pouch, and it contains toxic silicon beads.  Be careful not to tear it open.
2. Strong permanent magnets inside the triangular base of the read/write heads.  Theses are rare Earth magnets, and they're very strong.  Two of them could pinch fingers painfully, and disrupt/scramble cell phones, credit cards, or computer monitors.  They're great fun to play with, but they are much stronger than refrigerator magnets.

P.S. The hard drives were found on St. Louis Freecycle:
http://groups.yahoo.com/group/freecycle-stl/
and donated by ByteWorks:
http://byteworks.bworks.org/