A quick partition primer
I just finished installing OpenSUSE 10.2 on my laptop. While the process went without a hitch (image gallery of the install with instructions and potential stumbling blocks to follow later today) and SUSE even recognized my wireless cards immediately, I realized that a basic understanding of disk partitions would be helpful, whether you live in L'Unix-land or Windows World. So here goes (experienced partitioners need not read any further unless you'd like some training materials for other users).
Hard drives (the main storage area on your computer, generally composed of spinning magnetic platters) can be divided into sections for use by your operating system. To the user, these are seen as completely separate disk drives (in Windows at least; in L'Unix they appear as separate media). They can be used as different drives (e.g., one for media files and another for program files) and, depending upon your setup, you may be able to look at one or more of them from any given operating system.
Which leads us to the two most important uses of partitions. The first relates to security and the stability of the programs you run on your machine. Most Linux installations will offer to partition your drive for you and place user folders (generally "Home") on one partition and application data in another partition. This is generally considered best practice and you should let it happen. Windows neither tries to, nor can do this, so it's less of an issue.
The second really spiffy use of partitions is the installation of multiple operating systems. This is also known as dual-booting or multi-booting. The various incarnations of Ubuntu are particularly good at recognizing other operating systems (like Windows) and offering to repartition your drive to preserve the existing OS. Then, when you boot your computer, you are given the choice of OS (e.g., Ubuntu and Windows). While this requires that you have enough space on your hard drive to hold two separate systems, it gives you a great deal of flexibility and allows you to live with an operating system in a way that live CDs can't.
As always, there are two particular caveats. Partitions should not be used for backup purposes. For example, some users back up their My Documents folder onto another partition. This is useless since partitions actually reside on the same physical piece of hardware, even though they look like different drives to your operating system. Therefore, if one partition "crashes", then they all go. Rather, you should back up to CD, DVD, or an extra hard drive.
Secondly, unless you are using utilities like those included with Ubuntu, partitioning tends to be destructive to data. Windows Vista installations are especially vulnerable to corruption from resizing the partitions on which they reside. Thus, before messing with your partitions, ensure that any important data are backed up (not to another partition) and you have time to deal with some potential messes. In general, the process is fairly straight-forward if you are using the right tools. However, a few good backups mean that in the worst-case scenario you can "format" (erase and start over) your hard drives (or just individual partitions) and install the operating system of your choice. Without backups, partitioning hard drives can be a lot less fun.
Otherwise, happy happy partitioning! I'm off to finish restoring all of my backups to my freshly repartitioned laptop.