When it comes to dual booting, you need to have a more hands on approach during the install process. You can't expect the installer to just know what you want to have happen. It sounds to me that the /boot/grub/menu.lst
isn't set right. I would need to see it in order to help you further. The only thing I can think of is that the kernel can't find it's root directory.
The best I can figure, you have four partitions on your HDD. A boot partition, a swap partition, and two root partitions. The /boot partition can house several different kernels and support several different distributions as well. The swap partition can be used by any distribution. The two root partitions are obviously for each Linux distribution. I'll assume /dev/hda1 is /boot, /dev/hda2 is swap, /dev/hda3 is PCLOS' root partition, and /dev/hda4 is XUbuntu's root partition.
I just whipped up this mini-HOWTO now. Without knowing more about your system, I can't really offer any specific advice. All you can do is check to see if you've setup things right in comparison to what I've laid out here. Also, I don't know much about how either of your distributions expect things to be done. So don't get all uppity if there's something that doesn't conform to the PCLOS or XUbuntu way.
You'll need to run GRUB manually because it may get confused or not see the other distribution. You only need to run grub one time, so you don't have to keep running it every time you install another distribution.
# grub-install --no-floppy
grub> root (hd0,0)
grub> setup (hd0)
You'll need to edit this for every distribution you install or add. One thing to be sure of is that each Linux distribution has a unique name for the kernel image./boot/grub/menu.lst
# Which listing to boot as default. 0 is the first, 1 the second etc.
# How many seconds to wait before the default listing is booted.
# Nice, fat splash-image to spice things up :)
# Comment out if you don't have a graphics card installed or if you don't want a splash image
# This assumes that PCLOS' root directory is on /dev/hda3
kernel /boot/kernel-pclos root=/dev/hda3
# This assumes that XUbuntu's root directory is on /dev/hda4
kernel /boot/kernel-xubuntu root=/dev/hda4
You need to be sure that /etc/fstab
mounts the correct /dev/hda partition as the root for each distribution.
The only way we'll be able to help you is if you work with us. A LiveCD will certainly be able to read data of your hard drive. You'll even be able to do a copy/paste with the Web browser that's bundled with most LiveCDs.