Hi All,
Ive Just Bought An 11Week Old Male Staff Called Alfie :)
I Also Own A Female Shih-tzu, And I Was Wondering If Anybody Had Any Advice Of The Best Way To Introduce Them? They Arent Being Aggresive Towards Each Other, However Maisy (Shih-Ttzu) Has Become Quiet And Seems Withdrawn, Although I Have Shown Loads Of Affection Towards Her, Even More So Than The New Pup, Will This Change? Its Only The Second Day, Do I Just Give It Time?
Thanks, Kirsty.

this will be a shock for your first dog but if she isn't showing any aggression towards the puppy then thats a good sign. i would take things very slowly and give your girl plenty of space away from the pup as not all dogs like playful puppies around them. a stair gate on the kitchen is good as you can give the pup time out if he gets over excited and also so he can go to bed and rest.
make sure the pup doesn't try and jump on your girl as he needs to learn that this isn't acceptable unless she wants to play.   
don't expect too much too soon and i'm sure they will get on fine given time to get used to the situation. it took one of my dogs a few months to get used to my last pup but she didn't like her much.
i wouldn't sleep them together for now unless your very sure your girl is happy with the pup as she want have an escape rout to get away if she wants to.
i also wouldn't try an over compensate giving too much attention to your girl, just make sure she doesn't feel under pressure to be around the pup and stick to your normal routine of exercise for her and she can have plenty of your time then.
don't worry about things this will be fine soon but just keep on top of you pups excitement as he will be very strong as he gets older and a lot more powerful than your shih-tzu.
would be worth joining a good training class as soon as he's old enough so he gets lots of socialization and one to one training from you.
all the best,just try and enjoy things.  

I echo the above post.
Just to add, I brought my pup home when my last dog was 12 yrs old, it was a case of taking things slowly. I didn't allow them any time together for a few months without strict supervision and only when I was confidant that they could communicate properly (ie, the pup knew when to leave the oldie alone without me having to tell him) did I let them sleep in the same room, before then I used a stairgate to keep pup in the kitchen at night, or out of oldies way in the day when he wanted some peace. It ended up with oldie allowing pup to cuddle up to him in his bed (even though pup grew quick and was bigger than oldie by then!) :)
So yes, give it itme :)