No, you don't have to register your firearms within 24 hours! :banghead:
Statewide preemption went into effect in Nov. 2007. You only have to register in Clark county and only after 60 days.
Open carry is legal, but the NRA and local groups are having a tough time making North Las Vegas and Boulder abide by state law. You can open carry, but they may very well hassle you.
As for the car, with a handgun, you can carry loaded openly. You can carry loaded concealed as long as it is not on your person or in a bag/pouch/briefcase on your person. Put it loaded in a case on the floorboad and you'll be o.k.
As for traffic stops, don't ask, don't tell. Those of us with Nevada CCW's come back as having CCW's when they run us through the system anyway.
Have a good time but I would strongly encourage you to stay out of North Las Vegas!! Very bad crime rate. Watch for the street signs to go from green to blue and then get out of there!