How can I help my toddlers get used to having a new baby around?

Act natural. Don't make a big deal out of it. We all have to come to the realization that life changes.
Talk with him. Talk with him about the baby, but make special time for your toddler. Watch what you say- don't say "i can't play with you because i need to feed the baby". Say "i'll be happy to play with you in 10 minutes". Have some special books or toys your toddler can play with while you are nursing the baby- he can only use them at this time, so he will look forward to that time instead of resenting it.
Continue Routines . Toddlers have a comfort zone with routines. Obviously a new sibling is a major disruption, but trying to maintain routines such as eating and sleeping schedules, in addition to showing love and attention to the toddler go a long way in minimizing jealousy.
Love and attention. Having a new baby around can be traumatic for your other young children. They are not used to sharing mom and dad. Remember to give them lots of love and attention. This can be hard because parents are so focus on the newborn. Remember to include them and help them feel important.