Did you copy over the /boot/grub/menu.lst info from PCLOS? I'm dual-booting several versions of it with no problems. Easy solution is to boot Knoppix, access PCLOS menu.lst and then copy it into Fedora's /boot/grub/grub.conf Be sure to adjust your drive/partition information if it's been altered with the new Fedora install.
BTW, not to pass the buck but, this is really something that can be checked at PCLOS's Forum: http://www.pclinuxos.com/index.php?o..._smf&Itemid=58
since the boot problem really is within PCLOS, not Fedora.