Partition Windows (not working Help)

I am already running windows on my pc but i think about using Ubuntu as an second OS but I dont know how to create a mew partition. There are already 4 primary partitions installed on my only hard drive and if i try to make a new partition i get the message already 4 partitions installed.

Anyone can help?

If you are running windows 7, just download and run the Ubuntu installer, it will put a file on top of you C:/ drive, and give you the option of booting into Ubuntu when you turn it on, no partition required.