| Your 'df -h' output shows you are using less than 4GB of 36Gb so you have a lot of room there to resize that partition and create another partition on which to install your second. You can create a logical partition in your extended partition to install on. This should be sdb6.
If you want to use Grub from your current distro, when you get to the option to install bootloader, install to the /boot directory of the partition rather than the mbr. After the install, you will need to make an entry in the menu.lst of the original distro to be able to boot the new distro. | 
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