I like to create a /root partition of 15-20 gigs, a /home of at least 30 gig, with the swap of twice the ram, here, or at the end of the drive. Then I make the rest of the drive for data which both hard drives can share.Do the install of 2010 as usual, and when reaching the bootloader put it on the FIRST drive. It will then see all the operating systems on both drives,making the 2010 the default.If you wish you can make another the default OS by clicking modify, arrow down to your choice and click finish.At that point you will have to reboot, and will be prompted to take the disk out before the reboot. Upon reboot the older PCLOS will have a slighly different name with the new given name of the release. All this assumes that things have not changed upon the new release, although I think not as the same grub is being used.