Michael Crandall wants to know if dividing his hard drive into multiple, smaller partitions will improve its speed.
I seriously doubt it. In theory, a smaller partition could improve seek times with fragmented files, because the head has to move over a smaller space to get to the next fragment. On the other hand, smaller partitions can get more fragmented, which could slow them down.
But when you consider the seek times of modern drives, the whole thing becomes completely academic. Any speedup or slowdown will be too small to mean anything.
Not that there aren't good reasons to partition your drive. If you keep Windows and your applications on C:, and your data files (documents, music, application data, and so on) on D:, both are better protected.
Why? Because the best way to back up and protect Windows is with an image backup, which when restored returns the entire drive (or partition) to the state it was in when you made the backup. In case of a serious disaster, you may want to restore a Windows image backup that's several months old. But that will destroy any new data on the partition. With the data on D:, you can restore C: from an image and keep your data unchanged.
For more on the subject, see Move Your Data to a Safer, Separate Partition, Part 1: XP and Part 2: Vista.