Q) Why do some graphic files not Preview in the Insert... dialog box?
A) Page 2-11 of the ClarisWorks 2.0 Macintosh Getting Started Manual indicates that you can preview graphic files before using the Insert... command to insert them into your document. When you look at page 3-38 of the User's Guide, you can even see a preview of the Pegasus Logo (MacPaint) provided with the ClarisWorks Tutorial files. Unfortunately, this picture in the manual is misleading, and cannot be reproduced on your screen.
In reality, the Preview showing in the dialog box is based upon QuickTime's ability to preview the image. The preview checkbox and Create button in the Open and Insert dialog only show up if you have the QuickTime extension installed. Only PICT graphics and QuickTime movies can be previewed (the poster or preview frame of a QuickTime movie is a PICT graphic).