Sensors

I replaced some parts on my girlfriend's car. She has a 2006 Chevy Impala
Limited. Since I had to unplug some things to change out the parts, the car is
throwing up several sensors. Does anyone know how I can reset them to
make sure the parts work correctly? We don't have a tag on the car yet so I
can't take it into get it done and I'm not sure it will pass inspection with the
codes on the dash. These are the codes that are showing...

Service air bag   (i had to rebuild the front end due to a wreck by the
precious owner)
Service battery charging system   (i put a new battery in)
Change engine oil soon    ( i didn't reset it when i changed the oil last but
shop might do this one)
Hood open   (i replaced the front end after the previous owner had gotten
into a wreck)