Integrating Bootswatch Theme with Twitter-Bootstrap-Rails Gem
You only need to download the bootstrap.css file, and rename it. The bootstrap.min.css is the same as the css file just a minified version of it. Less is just another way of writing css and accessing each property differently. Check out less. Add css file and begin integrating into html, also point html to new stylesheet.
Here's a twitter bootstrap gem for easy Bootswatch theme integration/customization for rails: