It depends. Is the XP CD an upgrade CD, or a full version? If it's a full version, I believe that it will wipe your hd.
If that doesn't work, you'll need to create a boot disk, and hope that the computer checks your floppy drive before your hard drive. If you can boot from the boot disk, you can type "format c:" without the quotes, and that will wipe your hd.
If you format the drive, and your XP CD is an upgrade CD, you're going to need the Recovery CD that should have came with your computer.
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