K.
It's not productive to let your kid "cry for hours". However, it is likely that there will be a couple night's worth of crying involved whenever you change a kid's routine. I suggest reading the Ferber book on sleep (Solving your Child's Sleep Problems i think it's called). Basically, he recommends a "graduated" method of sleep training, which helps your kid learn to settle himself. Put your baby in the crib. If he's crying (and doesn't seem to be settling himself) come in after 5 minutes and calm him down. Let him know it's ok and that you're there. Don't pick him up. Then leave. If he's still crying after 10 minutes do the same. Repeat after 15 minutes and continue to repeat every 15 minutes until he falls asleep. This may take a whie the first night. Next night do the same. It will almost certainly be better the second night. I bet by night #3 he will hardly cry at all. We moved my daughter out of our bed around 8 months (though she sleeps with me if we're traveling) and it was the same routine.
Ferber's analogy to the routine change is, imagine you no longer have a pillow in your bed, or worse yet, you wake up in the middle of the night and someone's taken your pillow. This is unsettling and it takes some time to get used to.
ps: if you don't have the stomach to let him cry as long as 10 or 15 minutes, it's fine to keep these intervals shorter. like you could start going in every 2 minutes, then 5, and then 7 and don't go any longer than that. The next night you'd start by giving him 5 min, then 7, and then 10. Also, I find that sometimes it might be counterproductive to go in (ie you can tell he's settling down and seeing you is just going to wind him up again) - in that case just listen and wait out of sight