300 dpi is the standard res for print. The best advice is to scan as high(if you want high quality) as you can and then reduce the resolution and size in photoshop. Check with the printer or client what format they want the final image in(.eps,.jpg etc). Generally the image on your screen will look like the prited image - if your monitor is old or not calibrated properly(Use the Adobe Gamma soft' that comes with P'Shop) then try to look at the image on different monitors. If you are printing to a paper(as opposed a magazine), always tell the printer to 'knock back for press', this is because presses actually roll out the ink with a series of dots and any image will appear slightly darker. In a push you can do this in photoshop by applying a 15% white layer on top, but it's always best to let the printers do this.