Basically, you get the URL for the image by right clicking on the image and selecting properties. Then you post it on iHub by entering a left bracket ('['), the word 'chart', a right bracket (']'), the URL without the http and slashes (eg. chart.etrade.com/graphs/NOW.BIPH.d14.gif), then a left bracket followed by a forward slash ('[/'), the word 'chart', and a right bracket (']').
This lets me post a ClearStation chart for BIPH (a current fav) to get this: