loading images into CAPI

Hi

I have had a look at the entries with "image" in the name in the CAPI 
reference manual without figuring this out:

How do you read an image such as a jpeg, tiff, png, ppm etc. file and 
display it in CAPI?  Ie. how do you end up with an instance of gp:image 
representing your image file.

Secondly, the gp:read-external-image function that takes a filename and 
returns an instance of gp:image complains that "<filename> is not a DIB 
file" if I give it the filename for a ppm or tiff file. Neither gimp nor 
ImgeMagick can save images in "DIB" format. What is a "DIB file"?

    Kristian