It's true that higher dpi's result in a denser concetration of ink used by the printer, which can lead to more detailed work. A lot of it depends on the complexity of the design you're wnating to print, and how finely detailed it is. As we said earlier, 72ppi/dpi is fine for an image you're going to use for screenwork... but for print, you're obviously going to want something more. I tend to use 300-600 dpi on my home printer, because for an A4 sheet, on the apers I use, that's probably about as god as it's going to get. For a hih quality laser print job on a large sized poster, however, you might e best giving them a call and asking them what the best format is for you to use. You won't look stupid or naive - the fact you know what to ask shows you have some knowledge of the thing. But it saves you going in with an image saved at 15,000dpi (for example) ony to find out that 1500 would have been more than enough.

The other thing to bear in mind is that the more pixels per inch you have, the more data you're packing into that image - and so your image files can get pretty hairy. This is why when I'm working on my theatre company's publicity, I always save two versions of the image - one for print (either by myself or a pro printer's) at a higher resolution,  and one for emails, web, and so on squished down to 72dpi.

Jonthecelt