The Bottom Of This page, Get your Template
Looks like this
The resolution is 300 dpi. I devise photoshop actions to up-rez and re-size the art I want to use. Then I paste art into position and make PSDs. Levels of art in the sequence I typically visualize for the book.
PUBLISH Format Choice part of Lulu and upload it. Have your color covers separate but formatted in the same DPI etc. Lulu has an easy to use wizard for uploading the necessary files.
That's it. Easy.