excuse me, but I'd like to add my 2 penneth worth (2 cents worth, you American guys)
Part of my work is printing. I have spent A LONG time prepping images and files for print, and there are a few golden rules that make your output better, and make the printer happy.
1) printers HATE files in the wrong colour space, the wrong format and the wrong resolution.
2) see if you can talk to the people doing the printing, and ask them how they want the file prepared and sent to them (they love telling designers how to set stuff up, as it saves them (me) work.
3) it is an excellent idea to provide the printer with a hard copy proof. even in these days of PDF files (I hate them), sometimes unexpected things happen within the RIP software, so it's always good for the printer to have something on hand that shows him exactly what it is that you want.
4) Photoshop is probably not the best way to go about a print project like this. At least, not by itself. I would probably do all my image editing in photoshop, and then place the image into InDesign or Illustrator and create all the text and bar codes etc. in there. The text will be much sharper this way.
5) CMYK - it HAS to be CMYK. Do all your work in photoshop in RGB, but convert and save a copy as a CMYK file and use that for placing into InDesign/Illustrator.
6) Resolution - Steve up there states that photorealistic images are normally 240/300dpi. Sorry, but I disagree - Back in the day (the early 90's), "photorelaistic" was deemed to be >400dpi. This is the point at which your eyes cannot see the individual pixels in the image. I often create images that are to be printed at a high quality at 450dpi. I have also seen in the past images at 600 and 1200dpi.
6) The file you give to the printer. Once your artwork is set up, with all the bleeds, borders, gutters and printers' marks that are required, there's a 90% chance you'll be asked to provide a PDF file. Assuming that you've laid the images out in InDesign, you'll need to export as a PDF, or from Illustrator you can "save as" a PDF. My preference is to save an illustrator EPS file, and then render the PDF in acrobat professional. If you have images in the file, you'll need to be very careful of the settings - PDF's like to compress images a lot. they also tend to use the JPG compression format, which in my opinion SUCKS. I would suggest that you use the "pdf/a-1b:2005(cmyk)" settings for PDF's, but I change the compression for colour images so that it keeps them to 450dpi. This often makes for a large file, but print quality is kept.
Sorry if all that seems a bit intimidating! Talk to the printers - any print company worth using will advise you on how they want stuff set up. they may even have templates for you to use. Anybody who creates artwork for printing should certainly invest some time in learning at least some of the processes and problems that can crop up during printing. That way, you will rarely be disappointed with the output that you receive.
If there's anything specific relating to your print job, just send me a PM or an email, I'll try to help you out