For responsive design and frameworks, these are worth a look:
Adobe's Edge Reflow:
If you've ever used conditional css for IE browsers, then responsive design is roughly equivalent to that, except the conditions relate to screen size instead of browser, and are called Media Queries. I'm sure there's more to it, but that's in layman's terms.
If you want to do your own design for Wordpress, look for the Starkers theme, which is a bare bones theme that you can style fairly easily to match and blend in to an existing site.