I'm not quite sure what you mean by SEO a WP blog theme. You can go into the header file and add meta tags. Since it is a PHP file you'll have to open it in Notepad or Wordpad. WP has a plugin that will let you add Technorati tags in your post. There is also another plugin that will let you add Adsense to select posts. What other things were you wanting to do to your template?
You have 100% control over the theme so you can change the styles, h tags etc as you see fit. Do you want to give an example of a specific concern?
One SEO tip is to install the Optimal Title plugin - http://elasticdog.com/2004/09/optimal-title/ - which allows you to place keywords BEFORE the title of your blog in the page title (that's the bit that appears in the bar at the top of the browser window - it's very important for search engine results). This is quite important for SEO'ing each individual blog post you create.
No worries - glad the tip was helpful. It's often the simple things that matter the most and in my experience the title keywords are THE most important variable for SEO - at least they have the most *obvious* effect on where your pages appear in search results (the other things aren't so obvious).