http:// and www. URLs

I setup the site I am developing in such a way that the address http://stbees.org does work as does just simply stbees.org, but http://www.stbees.org doesn’t. I recall seeing something about this in the setup but unfortunately I can’t remeber where it was not whether it is possible, or advisable, to change it.
There are advantages and disadvantages to this. I frequently enter a URL as just the domain name – no http:// nor www. and mostly it works. The disadvantage is that some users will try http://www.domain and when it doesn’t work won’t think of trying the alternatives.