Guess adding this in Theme Options > Custom CSS does the trick:
img {max-width:100%; height:auto;}
.wp-caption {background:none; max-width: 100%;}
.wp-caption-text {text-align:center; word-wrap: break-word;}
.gallery-caption {background:none; max-width: 100%;}
.gallery-caption-text {text-align:center; word-wrap: break-word;}
Code like this should be in each WP stylesheet..
Guido