I think you should get slick tires for now, and when you get around to it (and have the means), you should get a full-on road bicycle.

Edit: I know your tires are 26" in diameter. You may want to get the same treads that I have. They come in 1.5" and 1.75" widths. See what the widths of your current tires are, and replace with the same width (so you don't have to buy new tubes).