You can add a partition in Windows Server 2008 R2 by following these steps:

Click 'Start' then 'Administrative Tools' and 'Computer Management’.
Go to 'Disk Management’.
Check to see if there's free disk space available.
Right-click on the 'Unallocated' space and Select 'New Simple Volume’.
Click 'Next’.
Choose what size the partition should be and click 'next’.
Choose a drive letter and click 'next’.
Here you can choose to format the new partition with either FAT32 or NTFS. We advise you choose NTFS as this is the better filesystem. The allocation unit size can be set to default or a custom unit size. You can enter a name for the partition under ‘Volume label’.
Check the 'Perform a quick format’ box and click 'next'.
Review the configuration and click 'finish' to complete the wizard.