Converting images to gradients?

Okay, I've searched literally *everywhere* in these memories, and there's no place that answers my question, so... Is it at all possible to convert images to gradients? Or maybe this is a better question: Why won't my PSP8 download certain .GRD files?? The gradients I'm trying to get are by crumblingwalls, in this entry. My PSP help thing says that it will take .GRD files, so why won't it take these?!

Argh. Seriously, I'm usually *very* competent when it comes to PSP, but when I'm not, it REALLY aggravates me.