I have never installed drywall before and I was wondering if I can use my regular cordless Black and Decker drill to drill drywall screws or do I need a special drill ??

 

they make screwguns that countersink the screw, but it's not necessary to use one. You should be fine as long as you stop before the screw goes all the way through the rock.

 

I just hung some drywall the other night with my cordless, Black and Decker. I also used it for laying plywood in my attic. You'll do fine, just be sure the battery's fully charged.

 

They sell adapters for you drill to use with drywall screws, which will help you keep from screwing the screws in to far. Not needed, but may help if you have never done it before.
You just want to get the screws in far enough to allow you to mud over them, without going to far and going all the way through the drywall.
You can use a cordless or corded drill.

 

Your gun is fine, you only screw the screw to the point where the paper dimples and the head of the screw is counter sunk below the surface. You do not want to drive the screw through the paper.

 

I have used the adapter and it works well. Worth the $10 for a DIY'er.