Pam, I am not Neal and don't play him on television, but I'll offer my
thoughts. I would record the voice over in mono, or just one channel and
use the options in Sound Forge to turn it into mono.
Then, place the cursor in Sound Forge where you want the voice over to be and use the merge function, control m, to pick the kind of voice over you wish. A fast duck means the underlying recording will duck in volume while your voice over is going. If you hit the right check box, it will then come back up after the voice over ends. You can just do a direct merge with the last choice in the merge menu, but be sure you adjust the faders or they will boost the pasted material and cut the destination material.
It isn't hard after you play just a bit and can produce some very professional sounding recordings.