As previously stated ignore the dpi. All Photoshop and other applications are doing in the image size dialogue box is indicating the size of the image,IF it were printed at 72dpi. It's only a guide, the file is not changed in anyway. It's the file size you need to be concerned about. 10 x 13 from a 40D should be fine for the size you want.
If it's like other applications I've used, the application that produces the pdf for printing will automatically take your image, size it for the page, and output at 250 dpi for final printing, all painlessly ( hopefully) .