Why does my iTunes use so much CPU time?

Here are some guesses:

• Indexing metadata about your music
• Pre-decoding next tracks in your playlist for smoother transition from song to song, such as gapless playback or crossfading
  • Did you recently enable gapless playback, and perhaps it is analyzing tracks for this?
• A bug

I'm seeing 0.0% load for a paused iTunes 10.6 64-bit on OS X 10.7 Lion.

Since you're using Leopard (OS X 10.5), maybe it's a Leopard-specific bug?

Sorry I don't have a concrete answer- it's a very complex thing, finding out what might be causing one person's Macbook to have issues running iTunes on an older version of the OS. Best of luck, though!