One rule of thumb you might want to keep in mind. The larger the original is the lower the dpi requirements would be to retain details. The smaller the original is the higher the dpi required because as its enlarged it will lose definition more quickly with a lower dpi. If definition is important then make your original as close in size to the anticipated printed product as you can. Be willing to give up dpi if you have to. Its the ratio of size difference between your work and the printed product which is most important. Remember most programs create fairly small pieces because normal screen sizes are in reality quite small if directly translated into actual print sizes. Most photos for instance are between 72 - 150 dpi with some occasionally going as high as 300 dpi. It would be very rare if it exceeded 300 dpi. Also most commercial printing, (dependent upon the process of course) is printed at a much lower dpi then you might expect. Because of the layering of ink, used to create the various color shades and blend them, a higher dpi sometimes works against you when translating to commercial printing. Again its the ratio of difference between the original work and printed product which is important. Most definitely talk to your printer before you make your piece.