First, make sure you are booting from the top drive, which is the master in a two optical drive system.
In the boot priority list, try removing all devices other than the CD drive. Then try booting again. You'll get the "no boot disk" error, but just keep hitting F1 to try again. If this disc is bootable, it will eventually work. You can verify that it's the disc, not the drive, by trying your XP reinstallation disc.