XP Dec '11: napping in crib

UAbride31007

So as of now DS sleeps fine in his crib but refuses to nap in it. I start him off in the swing unt he's asleep and leave him for 15-20 min and then put him in his crib. This works perfectly fine at night but during the day he wakes up immediately and is crying within 5 min. How do I get him to nap in his crib? Is he still too young? TIA