Not accurately, CSS has text-transform, which has 3 options, uppercase (which you don’t want), all lowercase, but it will remove all capital letters, even ones used correctly. Lastly, there is capitalize, which is as it suggested capitalize the first letter of each word, otherwise known as title case, for movies, books, albums etc.
Anyways, my quick solution would be to firstly lowercase everything, and then use the CSS3 :first-letter (may not work in IE6/7) to capitalize the first letter in a paragraph, however this will not look pretty if there are multiple sentences in a paragraph.
.comments p{text-transform:lowercase;}
.comments p:first-letter{text-transform:uppercase;}
I haven’t really searched for any solutions, you could try googling it, or search the plugins directory.
