A lot of people use WordPress to build and run their blogs.
A lot of people use Photoshop to mock-up an layout of their web site design and then use that layout to create the actual website layout, usually via some sort of grid.
There are a growing number of WordPress Theme frameworks than can be used as a starting point for WordPress blog design.
There aren’t really any WordPress-based PSD frameworks available for free. Not true.
The guys over at Area381, who I have never run across before today offer a WordPress PSD Framework file for free download.
Now, no matter how you start your website design, you have a solid jumping off point.