press enter before leaving the cell
Try pressing after you type in the variable name. I believe is normal behavior for Eclipse, but that a request to have it altered to not require a has been submitted.
I'm working through the same book right now and will be glad to assist you if you need any help.
Oops. RETURN is not displaying in my reply, but you probably get it point.
I did need to sync up with the project in CVS and rebuild to get some things to work as described in the book.
Using the ENTER key worked great! Thanks so much!