You can get more information and the download link from the Live Writer Blog post. You should know that the install does take quite a while to run through, and it installs new betas for other Live products you have installed.

The main new feature for Beta 3 is the ability to include images for blogger posts using Picasaweb. Below are screen shots of the install process and the updated live writer.

liveinstall liveinstall2

lwbeta3

P.S. If you've not used Picasaweb before you'll be prompted with the following when you try uploading images for the first time:

lwbeta3 - picasaweb

Just follow the prompts and everything will appear. If you've ever uploaded images to your blog via blogger before they will appear in your picasaweb album as well.