I find that Debian is good on the hard drive for old hardware, and even Knoppix will run for me with 200Mhz and 96MB RAM ( if you have swap space), but speed and usability is in the eyes of the beholder. All I have is old hardware, so I have tried lots of avenues and have settled on Debian/Knoppix. If you boot Knoppix with the cheatcode "knoppix desktop=icewm" you will have a fast desktop to work with. I would avoid KDE if you are going to use multimedia applications whether on a live cd or install, unless your Pentium 2 is 400Mhz or more.