Not exactly. The root, /home and swap are all different partitions, so you can't call it ONE partition. It's three.
But yes, if you later install another linux version using these same partitions, it will not affect Vista in any way, or any other partition on the disk.
You can create the partitions in advance with Gparted, but it's not needed since you can do it with the installer. In any case, you should have the 30GB unallocated space (not belonging to any partition) before you start. And not have reached the limit of 4 primary partitions.
From ubuntu live mode, can you open terminal and post the output of this command:
Code:
sudo parted -l (that's small L)
That will show us the existing disk layout.
If you install the grub2 bootloader to the MBR (which I recommend) it will overwrite the windows bootloader, but it's easy to restore it back even if you don't have a vista dvd. Making ubuntu boot with the windows bootloader is more complicated especially if your vista is not working good right now because of low resources.