I felt really guilty after my son was born (my daughter was two and a half and totally used getting every second of my attention). Here are a couple things that helped her "bond" with her little brother and helped with jealousy issues:
Whenever we referred to the new baby, we always would always refer to him as "your brother." Your brother needs a new diaper, I need to feed your brother, etc. I read somewhere that that helps with jealousy issues because they will see you taking care of something that is theirs too. It sounds strange but I think it helped.
I tried to plan something she really enjoyed doing during his nap time. As soon as he would go to sleep we would sit and do playdough, paint, etc. Sometimes it was tough because I really wanted to be getting other things done while the baby was sleeping but I think it really helped her to have my undivided attention.
I tired to really stress that the baby liked her. If he would smile or laugh when she was around I always made a big deal about it, I'd say something like "wow, he doesn't usually smile so big for me, how did he you get him to do that - he must really like you." If she would get a diaper for us or pick up his pacifer I would say something like "he is really lucky to have such a great big sister."
It's really tough, but try not to feel so guilty - you didn't do anything wrong! Just give him lots of positive attention and hopefully he will start feeling better about his new brother soon.