This tool allows you to install Steam skins on Linux the graphical way. It comes bundled with Ambiance and Radiance skins in two variants (with and without window buttons). The tool allows you to enable native-window borders so Steam fits your desktop very well. You can also install 3rd party skins and revert to the original.
For download please go to the homepage (http://iubuntu.cz/Steam). Even though the installer is available here for download as well, it may not be entirely up to date and must be unzipped before use since gamebanana.com restrictions.