For a start you need to share details - what version of Aperature and of iPhoto?
If you meet the minimum requirements you can open each library with the other program - which is the easiest solution - http://support.apple.com/kb/HT5260?viewlocale=en_US&locale=en_US
Larry - thanks as I had NOT read that article. I have Aperture 3.4.3 and iPhoto '11 9.4.2 so I'm all set there. I had opened the libraries before in each application BUT misunderstood what could or couldn't be done in each application!
So if I now understand it, I can switch & open my Aperture library in iPhoto (and vice versa also) , have access to the particular project of photos I wish to use in Calendar & Letterpress Cards, make these Calendars & Cards, buy & send off to Apple's Printed Services? Since I don't plan on doing any editing work in iPhoto for these photos, those iPhoto '11 created projects are only viewable there?