Now with iPhoto2 and iMovie3 out, I actually plan on using those iLife Apps. So I started to look deeper into why iPhoto refused to import the pictures from my digital camera. I have an Agfa CL30, and whenever I tried to import pictures from it it gave me "The files could not be imported (they may be an unrecognized file type or the files may not contain valid data)." Well, I knew that was incorrect, every other program that read JPEGs read these files.
The problem was that the EXIF headers in these files were mostly empty. EXIF headers contain information about the picture that the camera has filled in for you. The most useful of these fields is the date that the picture was taken. You can use jhead to remove those headers entirely. After I did that, iPhoto imported those pictures perfectly. So to remove the EXIF headers from your JPEGs:
./jhead -de /path-to/pictures/*
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030204071419519