How to connect dc fan without motor shield?

Hello there..

I want to run a dc motor fan, 4.5v. I have L298 motor shield but it already connected to 2 dc motor for my robots' tires. So, it means I can't connect the dc motor fan to L298 motor shield because it was fully utilize. Could you guys help me on how to connect the dc motor fan to arduino without using L298 motor shield?

Thanks.

On / off control or speed control?

And, if you grow impatient for help, I suggest spending a few minutes with Google. The question comes up rather frequently.