What is the fastest linux distribution that is optimized and compiled for athlon xp 2400+ for calculative purposes not sound or video?

A bare Slackware install would be good, although a bare Mandrake install would work fine as well. If you are new to Linux, go with Mandrake over Slack.

Gentoo would probably be the fastest.
But sincearly any distro could optimized to perform the same.

thanks guys. So you're saying a knoppix linux (the easiest I heard) can be recompiled to run just as fast as gentoo?
Could you give me a link to an online manual you read to learn how to do this?

p.s.- by the way, how DO you learn how to use linux anyway? it can't be all experimentation alone, because you have to learn basic commands. I'm a complete newbie here. all I know is a few commands like "ls" to list files, and "cd /bin" to enter a folder.

Unless you personally know someone who knows Linux, The way to learn is through research, looking at online manuals, trial and error, and asking on boards like this. Anyone who has learned Linux will tell you that Google is your best friend! Also go to LinuxQuestions.org and look for answers there.
Honestly, coming from a Windows environment, Linux can be really frustrating in the beginning, but once you get the hang of it, you'll never go back!