You're VERY close ....460 pixels is a great size for posting a picture - not too big and not too small....
also ...for something to try - this is very easy and will size and name your pics for you
http://bluefive.pair.com/free95.htm
Scroll to PixResizer……Download the program..it’s really small and very easy to install – Depending on the size of your image you just have to click ONE SIZE (USUALLY 50%) or 460 Pixels and it resizes it for you...
SAVE YOUR PICTURES AS JPEG’S or they will not show as thumbnails.