The disk part utility can't extend the o/s partition, so that is not an option here. But, I think you can with a 3rd party software like Partition Magic. If you don't want to buy anything though, live with 2 partitions.
I had a dual boot system with XP and Suse linux for a while and then recently I uninstalled Suse linux. The partitions for suse were on my Windows drive. I managed to delete the linux partitions using XP setup and write a new boot record but my Windows drive partition is still 40GB and there is another 40GB of unpartitioned space on the same drive.
I had a google around to see if there was a way to increase the size of my partition to 80gb. It seems there is a bit of a risk involved in doing this. There was one method which told me to use a tool on a Knoppix Live CD to resize it. So I downloaded the latest version of Knoppix and booted onto the DVD but it froze whilst Knoppix was booting up, so I have given up on that method.
Is there any other way to resize the partition with only a small risk of data loss? Or would you recommend that I just create a new partition on the same drive so I would have two 40GB partitions on my windows drive?