According to this info, you have 4 partitions. You would have to shrink any of the partitions.
Open a terminal and type gparted...If gparted is not onto BT5 DVD live, then you will have to download it and burn it in a CD and reboot with it.
Go to those partitions or the one you want to install BT5 on, format the partition and use an ext4 filesystem, or you can shrink the partition where you want to install BT5, and format it with ext4 filesystem. Also you need a small space for swap partition (about 1 or 2 gb). You will have to creat it, same thing.
Apply changes and then reboot with BT5.
Then try to make "manual installation"...