Unable to Complete Itunes Update


Software Update for ITunes presents this message: Update ITunes could not be verified and expanded correctly. Make sure you have permission to /tmp/501/Temporaryitem/com.appleSoftwareupdate. Then try again.

I've googled and read some answers for similar problems but hesitated on doing what seemed might work in this case, as it involved total and final trashing of trash contents.

Also, can you tell me why this problem occurs and if it could be why my computer is so very much slower than it even usually is with dialup?

Thank you,

Also, how can i attach the ipod to the computer and NOT have what's on it erased when the original file is no longer in the ITunes file?