Resolution cap for book printing

A couple years ago, an artist friend of mine was using I-photo to print portfolios. The results were so-so even though he was using high resolution images (300ppi).

Apparently, he found out that I-photo has an arbitrary cap on resolution around 200 ppi and will reduce images to this setting. Further more, he found that this could be fixed by opening a settings file and entering a high PPI. He did this and got better printing results.

I have lost touch with this person, so I can not ask him where the settings file is or how to alter it.

Can anyone shed some light on this for me?