How can I obtain a copy of my CD Reinstalling Operating System XP Home Edition

Hi: I bought a Dell computer in 2003 and now I need to reinstall the operating system. My computer don't have warranty right now. My CD for reinstalling the operating system crashes and I don't know how to obtain a copy of that CD. Someone told me to contact Dell because they can sell me a copy that will costs $25.00 aproximately because I bought to them the computer with the software. Is that true? Who should I contact? Can someone help me.