The reason you are unable to partition is that you are using the disk that you are trying to change (can't partition mounted volume). This is maybe not impossible, but definitely a dangerous thing to attempt. The best way to achieve what you want is to run a live-CD (knoppix is good for this) that has some partitioning software on it (qtparted in knoppix).
Is the 80GB disk one huge partition, or do you have some spare unused space? You will need some unused space if you want a new partition. qtparted can create this space by resizing your huge partition, so can parted, so can a commercial product called 'partition magic' (I think this runs on Windoze). But even if you do not need to resize, you will need to boot off some external media (CD or floppy) to create your new partition
You could try
if you don't know the answer to this question.
If you are using fdisk, use the 'p' command to p
rint the partition table as it currently is. Again, I advise that you do not attempt to modify the partitions if you are running from your hard-drive, but you can look at them without causing harm. Just look, then exit, do not choose the write