Wiping a computer and reinstalling OS.?

I have a Dell XPS that's kinda older. I got it for gaming, but it soon turned into a work/gaming computer. I've put pictures/spreadsheets/files that are needed from this computer to an external and now want to wipe the computer and start over just for gaming. I have a Dell DVD that is a reinstall for the OS (MS windows XP media center edition 2005 with Update Rollup 2). Also I have all the drive installation DVD's. Could anyone give me a step by step of how to wipe the computer then re-install the OS. I'm fairly computer illiterate:( Any help would be very appreciated