I agree with everyone else but I'll take a shot in the dark here. Does the book have it listed with the word this in front of the argument in the onmouseover and onmouseout event?

It seems to me that the script may need to know what object the function is referring to.

Just a guess from having a quick glance at the script.

Also your book should have a website with all the scripts available for download. You can DL it and check it against yours.

Good Luck,
Scott