My son started this around the same age. He was three. I did the same, pick him up and put him back in bed. I did this for about 5 months, it didn't work. I decided to change up the routine before bed a little. We started doing something physically demanding before and after we ate supper. I.E. walk around the block, run around the house, jump rope, hop scotch. Enough that they are getting good excersize, and using up their energy. I decided at this time to cut out his nap as well. He just didn't need it. About an hour before bed we would do something mentally challenging... flash cards, reading and writing skills. Followed with a bath with lavender, and nothing more to eat or drink after 7pm. I dimmed the lighting in the house around bath time as well. Certainly no sugars, juice, fruit, after supper. Then I would take him to bed, read for about 20 minutes. Durring this time I would let him get out of bed, walk around his room, ask questions about the book/s, but when they were finished it was time for bed. This helped 100%. I don't agree at all with letting children sleep with you. This is not a way of really dealling with the issue, just a temporary relief. Good luck.
I leave a light on in my son's room that may help. It sounds like he is scared of this new enviorment. Maybe you could leave a little TV playing his favorite video on at night for comfort. Make sure he has soft blankets, soft pajamas and stuffed animals to keep him company. My son loves it when I wrap him up like a burrito with some fleece blankets. I don't really like the idea of putting him back in the bed over and over again. I know what you are talking about because I saw it on Super Nanny, but didn't agree with it. All it does is exhaust the parent and child. There is nothing wrong with letting him sleep with you for a little while until he can feel more comfortable in his room.