The higher resolution the better I believe !!?
I only ever used to work with web compatable images and they are about 72 - 96 dpi (Dots Per Inch) but now use a max of 300dpi for a much better colour quality print - I think that's the minimum requirement a print company will ask for though !!
My business cards look cool but I've not seen them done any higher than the 300dpi - because I do a lot of downloadable graphics & files .... size matters
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Do you know any of the print guys that have a good explanation on all this ?