Sass for Designers
sonspring.com
sonspring.com
(a) You can convert the designer's CSS to Sass (designer CSS is going to be suboptimal anyways)
(b) You can convert some of the designer's CSS to Sass (the parts you're going to be "playing" with, like box and form styles) and leave the rest static.
(c) You can leave the designer's CSS intact as a static CSS file and then extend and override it with Sass.
One of the more common bits of Haml/Sass FUD is that "designers won't use it", which is true, but irrelevant.
(Having said all that: the last designer I worked with was excited to learn Sass, and did a great job with it).
Where is Linux?
For desktop use? In third place. Plus, most people on Linux know how to install new software. Finally, the package managers included with many popular distributions of Linux make finding and installing packages like Ruby so easy that it's not even worth describing how to do.