I know about resistors... but I don't stock 3W resistors, and this was a "half an hour project", well the circuit, and I took what I got. I'm going to buy some apropriate resistor this week, and hopefully design a standalone power suply. It's a "to-do" 
About driving the gate... I know it's "wrong" to put the resistors there, but just minutes before I found this MOSFET's, I had some power transistors there (and you should put a resistor between transistor's base and arduino, right), and I didn't remove the resistors after replacing them with MOSFET's. Are you sure about putting resistors between gate and vcc (or, as I would put it, between gate and ground)?
Thanks for the comment though!
Regards,
Peter