Notice Step 5 of http://www.blackviper.com/Articles/OS/InstallXPHome/installxphome1.htm show us able to delete and create a partition with the XP CD/Installer.
That effectively wipes the hard disk clean. Now we need the rest of the install plan but you need to check your SERVICE TAG number, head to dell.com and get their instructions on how to install the OS.
I want to delete everything on my computer and reinstall it. it is a dell dimension 2400 i know very little about this kind of stuff