1) Login to dashboard.
2) Go to Design -> Edit html (please backup your template before you make any changes).
3) Search for </head> tag.
4) Paste the code below on top of </head> tag.
<link href='your icon url' rel='shortcut icon' type='image/x-icon'/>5) Save Template.
It'll be great if you could find a good hosting for your icon. Picasa Web won't allow us to upload .ico file. ImageBoo does provide free hosting for icon however it's been blocked by proxy at my office (plus I've read some negative feedback somewhere about the service, then decided to use other alternative). Icon generated by IconJ was kind of ugly (probably to encourage people opting for the premium service).
Alternatively you could use .png image as your icon (which can be hosted on Picasa). However, it'll only work with Google Chrome and Mozilla Firefox. No luck for IE.
Icon file can be hosted at Google Sites.