K.J.
I'd start by (if you have enough space in the room) keeping his crib in there for night time sleeping. Have him start taking naps in his new bed. My 3.5 year old did have some sleep disruptions when he moved into his big bed, and REALLY tested my patience by continuously getting out of his bed. I used the technique that "Super Nanny" uses. Whenever he'd get out I'd just calmly and silently walk him back to his bed....over....and over...and over again....and again...and again. It took a few nights of walking him back to bed, but he eventually learned that he must sleep there at night.
You can also make a big deal of it by letting him help choose his new bedding. For my son, it'll be Cars or Toy Story once we move him into his twin bed in a few months. That has really helped him get excited about moving into a real bed (he currently sleeps in a toddler bed but needs to transition since baby #3 is coming soon.)