formatting

Hi .

im a total noob when it comes to computers .
I want to clear my hard disk I want to start fresh cause my computer has been running slow .

How can i do this can i just format the HD or will that remove windows as well ?

thanks

Any ideas on how to get an old windows install to get some of its old luster back?

To echo >>3 I've found both scheduling regular defrags (http://www.microsoft.com/windowsxp/using/setup/learnmore/tips/gehrke1.mspx) and removing spyware (spybot http://www.safer-networking.org/en/download/) to have significant benefits. Can anyone offer other tips?