If your hard drive is an external drive, connect it to the computer. Launch Disk Utility from the Applications:Utilities folder.
From the list on the left select the drive you would like to format
Click to select the Partition tab.
From the Volume Scheme dropdown select the number of partitions you would like to create on the drive.
Select a Partition (ie Untitled 1) then give it a Name, Format, and Size.
You can also drag the handle between the partition boxes to resize the partitions.
Select the remaining partitions and enter their Volume Information.
Note you can use the Plus and Minus buttons to add or remove partitions.
Press the Options... button to choose a partition scheme for the hard disk.
To use the disk to start up an Intel Mac select GUID Partition Table. To use the hard disk to start up a PowerPC Mac select Apple Partition Map. To use the disk to start up a Windows computer select Master Boot Record. Press the OK button to set this option.
Press the Apply button to begin partitioning.
A window will popup asking you to confirm the partitioning. Please note this will permanently erase all data from the disk. Click the Partition button to continue.
Notice the status bar shows the progress of the partitioning.
Once the partitioning is complete Disk Utility will update and show the new volume information for your hard disk!