I don't think linux is very fast. A well configured windows box can be just as fast and in many cases faster than a linux box. I have never done any overclocking, so I can't help you there. I just wanted to say something about those comments.
I just mean, you can run Linux on much slower machines than Windows, damn, now you're telling it; my comment didn't make any sense in this case.....

When I'm friends' houses they often have this super slow computers just because they have like 20 things opened by default in the taskbar(msn, yahoo, kazaa,...).
A friend of me has a 900MHZ (Intel Pentium III I think) box and it runs 10 times slower than my 485MHZ box.