I don't think they really "get it" at that age. But do go down to the children's library and ask the librarian for some recommended story books for young toddlers about this - whatever they don't have, they can borrow for you via interlibrary loan and you can pick up/return at your local branch. Read each one a couple of times but don't read every single night about this unless your due date is imminent.
If you haven't had someone else putting your son to bed besides you, branch out now! You want more than one caregiver completely familiar with the routine. If both parents are away during labor/delivery, then grandma or grandpa has to have your regular "drill" down pat.
And after the initial honeymoon period, many older siblings want you to give the new baby back to the hospital! It's typical and has nothing to do with whether or not you prepared well.
Sometimes there are sibling tours of the hospital - not sure how much a 14 month old will get out of that, but you can ask.
A lot of people have a few "big brother" gifts set aside so the baby doesn't get all the attention.
Other than the initial get-acquainted time, I agree with Sherry that they don't ultimately remember live without the sibling.
Good luck!