Microsoft included a disk partition tool in Windows Vista, which can be handy when you want to create a partition to boot another operating system from.
To partition a hard drive click the Windows button → All Programs → Administrative Tools → Computer Management. If the User Account Control window pops up click Continue. Select the Volume to work with, then right click the Volume, and left click Shrink Volume.

In the example below your new partition would be 2028 MB, or 2 GB.

Right click the new 2 GB partition, then left click New Simple Volume.

We will format the File system as NTFS, and choose a Volume label, which can be anything, but it’s best to keep it short. Click Next.

You will be able to see the status of the formatting job for your 2 GB partition.

Once the formatting is complete you can start using your new hard disk drive partition just as if it was another hard drive. You can install another operating system to boot from, or usage for storage.