book - two sides

[Giuseppe Vitalone]

Hi, I use Lyx 1.5rc1 in Windows. The guide says that the class "book" make
the new chapters start on the right page, but in my documents it doesn't
works, new chapters start on the left (in fact, right margin is wider), why?
I can't attach any source to this message, but I will send it to anyone who
can help me.
Thanks