adding www to url thru htaccess problem

Hi, i’ve tried several scripts for my .htaccess that add the www. prefix to the url, when it is not typed in. but this somehow conflicted with wordpress, wierd things would happen. now does anybody know what i can put in my .htaccess file that adds the www. prefix to the url when it is not typed in, and does NOT affect wp? the problem was, when i’d go do leave a comment, after submitting, it’d take me to a blank page and the comment wouldn’t be saved. NOW i’ve noticed that when i type myurl.com/blog it automatically adds the www. even with an empty .htaccess. but i’d want it to do that outside of the blog as well, so i see two solutions: 1) a code that adds www. to all url’s except url.com/blog, OR (my preffered)
2) removing the script inside of wordpress that adds it. if it is not vital to the operation of wp, i’d like to remove the code myself. thanks in advance!