Seeing as SimpleViewerAdmin doesn't seem to be actively maintained, I'm having a crack and updating it to be compatible with SimpleViewer 1.8.
Once it's decent, I'll chase down the author and see what's what.
Anyway, so far everything looks good, except that albums are a little buggy in Firefox. Sometimes the thumbs display, sometimes not. The main image very rarely displays.
There's an example of the problem here: http://benhughes.awardspace.com/testbed/?album=Album2
The call to viewer.swf looks good to me, and the 'open in new window' links work, so the images exist. The paths also look correct, including case.
Anyone have any ideas?