Summarize:

This will begin the setup process. If you're prompted to press a different key, press that key instead of F8. Doing so bypasses the repair process. This line of text will say something like "Partition 2 (Windows)". Press the ↓ key until this line of text is selected. This will delete the partition where your operating system and all of its files are stored. You may see slightly different key prompts at the bottom of the screen. If so, use those instead. There should be a blank space where the partition used to be; make sure it's selected. This will create a new, empty partition in the space where the old one was. Doing so will select the partition as the location to install Windows XP. Select the Format the partition by using the NTFS file system (Quick) option using the arrow keys, then press ↵ Enter. This can take several hours. Once this process is complete, you'll follow the on-screen instructions to reinstall Windows XP; however, your files, programs, and any other user-installed items will be gone. You will need your product key to finish installing Windows XP.
Press ↵ Enter at the "Welcome to Setup" screen. Press F8 to accept the Windows agreement. Press Esc when prompted. Select the "Windows" partition. Press D, then press L. Re-select the partition's space if necessary. Press C, then press ↵ Enter. Select the new partition and press ↵ Enter. Choose NTFS as the partition's format. Wait for your hard drive to finish formatting.