Sorry to hear of your difficulties HelenEmjay. MY dd is also two weeks old, and ds is 2.5yo.
Although he is taking it out on other people, I think your ds is probably frustrated with you and dh, now that you have another baby.
One thing that I think really helped us, is tht I told everyone NOT to make a fuss of dd in front of ds. So we all are very low key about dd in front of ds (although we adore her out loud as soon as he is not around!)
Also, making sure that all the important people in his life have some time alone with him (my dh is great about taking dd from me so that I can do "normal" things with ds like get him dressed etc). the grandparents also do things with ds on his own, including taking him out of the house for a treat eg walk in the park.
I am finding that ds is wanting to spend a lot of time with dh, and they are doing "boy things" together like going for walks. We have also made bed time more fun for ds (he's always been pretty good about going to bed), letting him ride "daddy horse" (or "mummy horse" if I'm not bf) to the bathroom to clean teeth, and then from the bathroom to the bedroom. He just loves it. Daddy horse is very good and sometimes does a couple of laps around the house first - and sometimes will do a lap or two just for the heck of it when it isn't even bedtime. It is a small thing, but it is something that baby can't participate in, and it makes ds feel special (and he has fun).
dd also "bought" ds some gifts including water pistols (a big hit at bath time) and a leappad (an interactive story/game book). This was pricey, but helps keep him occupied while I bf.
Also, I let ds get on my lap even when dd is on me (usually bf), and I read to ds while bf (if he seems to want to get close to me).
Plus telling him how she loves him and is delighted to have him for a brother.