Forgot partitioning of drives while formatting

I am a windows 7 user and I recently had to format windows vista from an old laptop I hadn't used from a long time. So I installed windows 7 but forgot to make partitions of drives like C,D,E etc. After the complete installation, I tried to make partitions by going to my computers but I had no idea how to do it. Is there anyway to make partitions after installation or do I have to install it again?
