Help texturing book

Hi, I'm trying to texture covers for book models; I just select all the book, use multiSubObjects, add a different ID number to each book cover and apply a different bitmap to each. But as you can see in the picture, the top and bottom parts are fine, but the middle part is not. Is there something I'm doing wrong, or is there a simple and fast way in doing it, because I have about 50 books to texture with a different cover each.
To see the images of what I mean email me.
Thanks for the help.

I found an online tutorial at viscorbel.
Might be useful for someone.
Bye!