What size should a digital picture be for best printer/copier results?

We have a Canon Image Runner printer/copier/scan/fax. What size should a digital picture be shot with a Casio Exilim 7.2 megapixel camera for best results. I want to get as many pictures on a memory card as possible so I don’t want to make a picture larger than necessary.

It depends on what size you want to print them at. Good quality prints are 300dpi, so if you want a 4×6" print, you need at least 1200×1800 pixels (about 2.2 MegaPixels). Obviously if you want to print 8×10′s or larger prints, you need proportionally larger image files.