1. Slide a thin, non-marring tool such as a fingernail under the top edge of the keycap.
Depress the bottom edge of the keycap.
Rotate the keycap up with increasing pressure until the two top clips are released from the scissor.
Invert the keyboard and jiggle the key to release the lower hinges.
Drop the keycap into place.
Jiggle the key to seat the lower pivots.
Press down with increasing pressure until the top clips click into place.
You can get a key here at amazingly high prices: http://www.welovemacs.com/apwialreke.htm...
Consider searching eBay for a better price. Look for Apple Aluminum Replacement Keys. I found four listing for under $5
UPDATE - Here's the teardown of the keyboard I did last night: Apple Wireless Keyboard (A1255) Teardown
This simple fixit text did me good!
Even a slightly-marring tool helped me, a small flathead screwdriver for lifting up the top part of the H- and J-key, until I got a better grip with just my fingers - wiggle, and pop! The key cap came off. (I got my hands of a wireless keyboard where the H and J keys were switched, for some crazy reason) and now it workes like a charm. I just popped the caps back onto the two keybases again, "k-pop, k-pop". Lovely.