What's your power source? (You don't need a 6V regulator.)
I am assuming that I can power the mini pump which is 3V directly from the board (5V) by adding some resistors.
No. You need a 3V power source (or a 3V regulator) and a driver circuit, both capable of more than 1 Amp (5W at 3V is 1.67 Amps).
You'll need something "bigger" than a 2N2222, and unless you're using a pair of 1.5V batteries you'll need a 3V voltage regulator.
[u]Here[/u] is a transistor driver circuit and [u]here[/u] is a similar MOSFET driver. In your case, either of these circuits would be connected to 3V as required by your pump.
If you're building a 3V voltage regulator you should build a switching regulator (which is a bit more complicated and requires an inductor). A linear regulator (such as the LM7806) will usually overheat if you try to get 1A or more out of it (depending on how much voltage you're "dropping" across the regulator and depending on the heatsink you're using). ...I don't think they make a 7803 (3V version) but you can get similar "adjustable" regulators. [/color]