Note also that the print resolution required depends on how close you will be viewing it.
The company I work for had a trade stand at the recent AOG Conference (Australasian Oil & Gas), we wanted to exhibit one of our products but it's size was a serious headache. The next plan was to photograph it and have a life size print made.
Due to it's size, I stitched two 18mpix photo's together vertically in MicrosoftICE to make a ~26 megapixel image, this was then printed as a 2.4 by 2.4metre foamboard poster and placed on the back wall of our trade stand.
At 2.4m the print scale was approx two pixels per mm, or around 50dpi. The visitors would walk past the stand no closer than ~3 metres to the poster and by all reports I got, the poster looked amazing. I was too busy to attend and see it for myself unfortunately
