I recently had to replace the alternator in my 95 nissan altima and when I started it up the airbag light started flashing. A friend told me to disconnect the positive cable and to ground it directly to the negative post for a few minutes and that that would reset it, but that didn't work. If anyone can help me with this that would be great. Thank you.

It is possible that during the alternator, the Diagnostic Sensing Unit may have gotten an inadvertent voltage spike when the power was restored to the car.
Clearing the codes without a proper scan tool is difficult.
Try these steps:
Attachment 28027
When they say driver's door switch, I believe they are referring to the door lock switch.
If this doesn't help, you may need to contact your local dealer or other shop that deals with this type of problem.