Actually your question is already answered in the very first thread in this forum, please try to check to make sure no one has already asked your question, before posting it You'll usually end up saving yourself some time if the answers are already there.
But to make things quick for you, there's no button to do that, so you have to fiddle a little bit with URLs:
QUOTE: Hover over the "RSS" of the comic to get the comic account number (it will display in the status area at the bottom of your page. The grey area that usually reads "Done" ). It would look like this:
http://www.drunkduck.com/rss/rss.php?cid=423
423, in this case is the comic account number.
Then just paste it into the URL that mapaghimagsik gave everyone: