karma, i have a 2.4 yr old and a 4 mth old, when i was pg with dd2 i was really worried too. i didnt speak much about the new baby when i was pg, dd1 didnt seem to understand much anyway. when i went into hospital mum looked after dd1, and she was very good, speaking about how dd1 was going to have a new baby in the house, she spoke very excitedly and dd1 got very excited too. when dd2 was born, mum took dd1 to the shops on the way to the hospital and said 'we are going to buy a new hat for your baby sister' dd1 was so excited. i think it helped that my mum kept saying 'your baby sister, your baby sister'
when dd2 came into the ward, she stood at the door and shouted 'wheres my baby sister' and ran over and covered her in kisses. she was so over-excited that she was a bit ott, grabbing dd2, kissing her really hard, etc. i was careful not to give dd1 into trouble for being rough, i gently explained she was only a little baby, etc etc and dd1 is now very gentle.
when we got home i never had a minutes peace to be with the new baby on my own, i had to include dd1 in everything and when i was feeding etc dd1 had to be there, almost sitting on top of the 2 of us, but i made sure she was included in everything, explained everything i was doing, let her give dd2 kisses whenever she wanted etc. if she woke dd2 with kisses, i didnt give her into trouble. it was very very hard but now after 4 mths i still have a clingy dd1 but she is not clingy to me - shes clingy to her baby sister! she always has to sit beside her, if i am changing nappies she has to be there to wipe dd2's bum etc.
it hard work but worth it when dd1 says 'i love my baby sister'
i think if you make everything fun, eg, when your new baby does something, even a small thing, like a big burp, say to your ds 'WOW did you hear that BIG BURP' and laugh hysterically, it is something you are doing together (oh dear that sounds stupid, i hope you know what i mean)
just now during the day its hard when im trying to get the baby settled down for a nap and dd1 is yelling 'mummy come and do my puzzle' but when dd2 gets to sleep eventually i say to dd1 'babys asleep, come on. lets go and play'
she gets excited at that.
you dont get to cuddle your 2nd baby on your own as much as the 1st time, but wait til your ds is in bed and then get your cuddle time then with your new baby
hth and good luck