|As a minimum you will need to do a repair install.|
Before trying to boot up the 80g drive in the P4 you should check bios to make sure the CD is set as first boot device. Insert your XP Install disk and boot up. You should get a prompt asking if you wish to install or repair. Select Install at this first prompt since the first R prompt is for Repair Console which is not what you want.
After it loads setup files it will detect your existing XP again and ask if you want to repair this. YES. It will then do an "Over-the-top" installation and you will lose recent updates but should retain programs & user profiles
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