WordPress Design Challenge

The transition of this site to some sort of content management system is long overdue. There’s too much stuff here now to keep good track of it manually.
I’ve settled on WordPress, given its ease of use and flexibility, and after the learned advice of technically-inclined friends. However, before beginning the actual site migration, it behooves me to cement the design of the new site first.
To tell the truth, I like the simplicity of the current design, though I have plans for the sidebar. What I’d like to do is modify a WordPress theme to mimic what you see now as closely as possible. However, my semi-random hacking at stylesheets and other theme components leads to broken sh*t. Anybody out there with design skillz who can help?