your post is rather confusing, but I gather that you either need to crop or add filler to make it use the dimensions you have specified.
this should fill
[CODE]convert -resize 1024x768 -bordercolor black wallpapers/47-1280x1024-f430spider05.jpg wallpapers/test.jpg[/CODE]
this will force
[CODE]convert -resize 1024x768! wallpapers/47-1280x1024-f430spider05.jpg wallpapers/test.jpg[/CODE]