tinyfeet, my dd was 18 months when I had ds. Obviously her vocab etc was very limited but we told her that there was a baby in mummys tummy etc, and would she like to put her hand on the baby while she had a story etc but didn't make a big thing of it, just made her aware.
I had to go in to be induced so she was shifted around a lot on the actual day, I went into hospital in the evening and dh put her to bed, we told her that mummy was going to get the baby but she might be a long time. DH had to come to the hospital at 5am so our neighbour got her up and then later a friend picked her up and took her off to play with her ds all day.
I came home in the afternoon (went for 6 hour discharge and had really good rest at home) and dd came back and we showed her ds, let her stroke his head etc and gave her a present from him.
She was absolutely fine, I just made sure that she was included in everything to begin with, if ds had to be fed, then she could have a biscuit and story sitting next to us, she helped bath him, picked his clothes etc.
I didn't move her room around until we bought her a bed and then made a thing of big girls, big beds, new rooms, she was about 2.3.
One thing though my ds is nearly 2 and although he has a very limited vocab he understands EVERYTHING! And don't worry about balancing 2 children, I was amazed that I had forgotten how easy tiny babies are. They eat, sleep and poo! And if you have to give dd attention it doesn't matter if the baby screams a bit.
The other thing that I think, and this is only my opinion, is that conflict arises when the older child is passed over all the time. I tried really hard to make sure that her needs were dealt with before ds (not spoiling her I hasten to add) and when visitors came if they paid too much attention to the baby, I got down and played with her so that she didn't feel left out.
Siblings will fight, mine started when ds started pinching her toys! But generally they are fine now.