Here is a good article on DPI. It talks about what it is and how it differs for print and on screen. The print info is towards the bottom, but I recommend reading the whole article.
http://www.danrichard.com/2006/03/23/to-print-or-not-to-print-making-sense-of-the-dpi-equation/
Remember Professor Harper recommends 300 dpi for print and 200 dpi as a minimum. Oh, and save as a tiff. InDesign really likes that file format.
