This is a really simple plugin that is probably redundant now that most browsers will pick up a favicon if it is in the root of your site but I have had this in my dev folder for quite a while so I thought I better get round to releasing it. Basically all it does is put the correct html code in the header of your skin to point to you favicon. It can be useful if you want to keep your favicon file in a different folder that the root of your site.
Download the Favicon Plugin, upload it to your plugins folder and install it via the Global Settings tab. Read the readme file and update your settings. Post a comment here with any questions.