For the visitor question, you could teach her down/stay on a little carpet. I suggest the carpet b/c you can easily move it from room to room and the dog will know that it is her spot to "chill" when there are visitors. I would also make sure that the dog is exercised before the visitors arrived if at all possible. As well, sometimes we buy a nice bone for our doggy to chomp on outside when we have visitors (not really a good idea though if you always have visitors - don't want a chubby puppy!).
ooo, just remembered - we've also taught our dog an 'all done' command. When finished playing with him, I sweep my arms across my body and say "all done" then ignore him. He gets the message that the game is done and goes off to amuse himself.
In regards to a new baby, this is what we did for our dog:
1. once the baby's room is set up, keep a bowl of dog treats in there. Every time the dog goes in, give a treat. This is to associate the room with good things.
2. before I brought DS home, DH brought home a blanket that the baby's smell was on so the dog could have a good sniff
3. when we actually brought DS home, I had DH let the dog sniff him. I didn't b/c I thought that I might be too nervous which the dog could definitely pick up on. As well, since I had been away, the dog was excited to see me and since I didn't have babe in arms I could give him a good cuddle as soon as I got in the door.
4. whenever I had DS playing on the floor, the dog was not allowed in the room. I always made sure that DS was physically higher than the dog
Those ideas can be modified of course depending on your birth or sleeping plans (ie homebirth, co-sleeping etc)