Provided by Microsoft Support, a step-by-step guide on how to create a partition on Windows Vista or Windows 7. As described:
Microsoft Support: How to re-partition without destroying the data?
We received a call: The system is installed on my machine. But there's only one partition. I don't want to reinstall the system to re-partition. Is it possible to create another partition?
This might be a problem that troubles many users. Generally, some third party software can provide such features. However, now Windows Vista/Windows 7 enables you to make some certain degree of adjustments towards current partition sizes.
Microsoft Support: How to re-partition without destroying the data?