page sequence....

A section of my Content Management system allows the user to enter pages (to be displayed in a popup screen) The navigation is based on page number, so the user must enter the page number when filling in the form. In the entry form I have an edit box (int) for the page number that must be filled. I don't want this to be auto incremented because the user is allowed to order the pages as they wish. Has anyone got a good solution to this (page numbering)? Begins with one and has max number equal to number of rows, page number must be unique etc. At the moment I just display a warning message based on total number of pages, this is displayed on an overview page of all entries. Thanks