To keep a correct ratio between themes, to do your screenshot,
first resize your browser so that the webpage will use a
-rectangular area of 640x480; then resize it 192x144.
+rectangular area of 800x600, and use appropriate images sizes
+(most probable "small"); then resize it to 192x144.
It would be best if the screenshots would show the same contents,
so just send me your theme if you create a new one and I'll do