I agree with WPRealty…there are many nice blog themes on the internet that you can get for free or pay for a premium blog theme. The process of converting your site over to a blog is not too easy if you are unfamiliar with the process. Depending on how many pages you have in your site, it will take some time to migrate those pages over to a blog. If you are looking to take advantage of the SEO benefits of a blog, you may want to think about creating a sub-directory and installing Wordpress in that directory along with the blog theme of your choice.