A drive on the desktop

As you'll know, inserting a CD ROM into the CD ROM drive causes it to appear on your desktop. In my system I have a second hard drive which also appears on my desktop as long as it's connected. Unfortunately, I can't remember how I originally set this up but I don't think it was as simple as just creating a shortcut. I've a feeling that I edited a config file somewhere. I'm now trying to set up my laptop comupter in the same way. Can anyone think what file I might have edited (or what I might have done) to make this icon appear?