Firstly, let's look at what exactly a harddrive partition is:

As the name indicates, a hard drive partition is part of the drive, or a section, treated by the operating system as an independent storage area or drive. Hence, a 120-gigabyte (GB) drive can be partitioned into several drives, rather than being used as one large drive.

This is handy for a number of reasons: 

You can partition your harddrive into multiple volumes, so that you can run more than one operating system on the same harddrive. This is also called dual booting.

You can have one harddrive act as two harddrives, to give yourself more storage options.

You can keep your OS (Operating system) separate from your programs, by installing your OS on one partition, and your software on another. Should you need to format, you only have to reinstall your OS, and not all of your software.

Understand these terms before you go on: 

•  Partition, partitioning: Free space on a hard disk must be partitioned before it can be used by an operating system. Creating a partition reserves a physical portion of the hard drive space for use as a logical drive, or volume, that the operating system can address. 

• Volume: A volume is how the operating system 'sees' your free disk space. Volumes (also called logical drives) are represented in Windows by drive letters such as C:, E:, etc. Volumes are formed by partitioning the free space of a hard drive. Volumes must be formatted with a file system before data can be stored on them. 

• Formatting: Formatting is the act of creating a file system on a volume, so that the operating system can store and retrieve data on that volume. 

• File system: A file system provides a means of organizing and retrieving information written to a hard disk or any other storage medium. A file system is created on a volume when it is formatted. Common Windows file systems include FAT32 (File Allocation Table 32) and NTFS (NT File System). 

The different types of harddrives:

What kind of harddrive are you dealing with? Is it a traditional parallel ATA drive (also referred to as IDE) or a newer Serial ATA (SATA) hard drive? The simplest and most reliable way to determine whether a hard drive is a Serial ATA or Parallel ATA device is look at the back of the unit where the connections are.

IDE: A parallel ATA, or IDE drive (still the most common variety) will have a 40-pin parallel ATA connector (a wide, flat, and normally grey cable), jumpers, and 4-pin molex power socket. The drive is 3.5" wide, and a little less than 1" thick.

SATA: Serial ATA hard drives are physically the same shape and size, and differ only in the type of electrical connectors they require to interface with the motherboard. The SATA connector cable is much smaller in width than a IDE cable (about 1.5cm). The power cable also looks different than the normal molex connector (that your cd/dvd drive uses for power, for example.)

Understanding the basics

In order to know how to unpartition a drive, you need to first learn how to PARTITION a drive.

 This is the easy part. Pop in your Win2K or XP CD and reboot the computer. You should get the option to 'press any key to boot from CD.' If you do not see this, you may have to go into the BIOS setup (by pressing the 'del' key upon rebooting) and make sure that your CD is selected as a boot device. This option is generally found in the 'advanced BIOS setup' menu option in the BIOS screen.   Once you have begun the installation procedure, relax and follow the prompts. You will be shown your available drives and prompted to create, size and format partitions on them as part of the installation process. Nothing outside the install needs to be done unless you opt not to use the full space of your new drive for installing Windows.

NOTE:

You can also delete partitions/unpartition a drive from this screen. Care should be taken though, as them moment you delete a partition, ALL data that may be on it will be lost indefinately.  If you have left space free on your new drive, once the installation is finished you will need to go into disk manager by right clicking 'my computer' and selecting 'manage.' Once you are in the management screen, select 'disk management.' From here, the unpartitioned space on your hard disk can be seen as the black 'unpartitioned space' section in the graphic display. Simply right click the unused space and select 'new partition' to use this space. The wizard will walk you through creating, sizing and formatting the partition with NTFS or FAT32.