diskmgmt.msc, and press
Partition of Hard Drive in Windows Vista
To create a new partition (Vista calls it a "volume"), click the Start button, type
to open the Disk Management utility. To create space for a new volume, right-click an existing volume and choose Shrink Volume. Vista will calculate the amount of space you can regain and will open a dialog box where you can enter the size of your new volume. (You'll also see the total size before the shrink, the maximum shrink available, and the size of the old volume after the shrink.) After shrinking, right-click the new "Unallocated" space represented in the program and choose New Simple Volume. Then follow the wizard's steps to create and format your new volume. When you're done, you'll see your new volume represented in Disk Management's graphs. Note that you can shrink only volumes that use the NTFS drive format.