Now OpenELEC lets you carry your HTPC with you in your USB drive. OpenELEC  (Open Embedded Linux Entertainment Center) is a HTPC software based on the ultra popular, the hip and chic XBMC (Xbox Media Center) and supports full HD playback to your television with support for video and sound over the HDMI port for easy connectivity. The latest release of OpenELEC 1.0 (1.0.2)  is based on XBMC dharma and looks like Dharma and behaves likes it, but what sets is apart from a full blown Linux running XBMC or the XBMC Live (Ubuntu based) is the following
OpenELEC is a small Linux distribution built from scratch as a platform to turn your computer into a complete XBMC media center. OpenELEC is designed to make your system boot as fast as possible and the install is so easy that anyone can turn a blank PC into a media machine in less than 15 minutes.
So, if you have an old laptop or PC lying around which doesn’t have much juice left to make it of any practical use, then give it a new life with OpenELEC. It supports a wide range of hardware  and the installation is super fast, you don’t even need to have a hard drive to install it, it just flies off right from a USB drive, you can add all your multimedia via external drives or access them through your LAN. For detailed installation notes and detailed setup guides visit this link . We ran it through its paces and it felt very nifty and light with smooth playbacks on an old laptop.