This tutorial was adapted from a tutorial developed by Mike Matas. We're going to use iPhoto and Photoshop to make a poster like the one here. The first step is to make a new album in iPhoto with the 98 photos you want to use. Try to make them varied in color...if they're all the same looking your poster will be boring.
Move the cropping box around to where you want it, and then hit "Crop". Do this for each of the photos in your poster.
Again, make sure that you're cropping in Landscape, not Portrait. This means that the crop is wider than it is tall.
Now, open that PDF in Photoshop. In the dialog box you see when you open the file (it won't open directly, but shows you this dialog first), set the resolution to 200 pixels/inch.
Photoshop will Rasterize the image. It takes a long time, be patient.
Once open, save that file as a TIFF.
Import the TIFF into iPhoto, select it and choose "Order Prints".
Select the number of 20x30 prints you want, and click "Buy Now".
Your print(s) will arrive in a couple of days.
Coming Soon!: A Photoshop only version of this tutorial.