The File > Print with Preview dialog box shows you how your image fits on the printer and paper size that’s selected, and lets you position the image on the page. By double-checking the document in Print with Preview before printing, you can avoid just about all wasted print jobs caused by incorrect image size, paper size, or orientation. While you’re in Print with Preview, click Page Setup to confirm that the printer and paper size are correct. The margins you see in Print with Preview are supplied by the selected printer driver, not Photoshop.
The Print with Preview dialog box has a Print button, so you can go straight to the Print dialog box from there. For this reason, you might want to use the keyboard shortcut editor (Edit > Keyboard Shortcuts) to assign Command/Ctrl+P to the Print with Preview command instead of the Print command.
Note that in Photoshop CS3, the Print with Preview dialog box is now the default print dialog box.