If your iBook's been opened many times (Like mine has been) then this piece may be broken.
If it's cracked down the middle or a little off, what you'll want to do is use your bent paperclip from a few steps later (or another screwdriver) and pull the second piece away from the shell when you start lifting. should pull right out
When re-installing use something sticky on your screwdriver to hold the screw in place, or it's never going in. The sleep magnet is nasty at grabbing your screw and pulling it away. (Doesn't hurt to have something sticky on it for taking it out too...)
It is alot easier to get at after you pull the speaker cable out. Use something small to pop it out of place though, I broke my extra spare being a little too hasty.