Hmmn.. I co-slept with my 2 yr old until he was a little over a year, and then he got a crib. He slept better and so did we. He's a really light sleeper and everything and anything will wake him up and he'll toss and turn. Anyway, we got him a big boy bed a couple of months ago, and some of the time he sleeps in that for naps.
Owen MUST get his nap everyday or he goes into unconsolable crying rages and can't function. I take him upstairs for his nap between 3-3:30 everyday (unless we're out but I try to get home for naptime). He knows this routine very well, and though he's tried to fight it, I will talk gently to him about how he needs his naps. I don't have time to lay down with him because this is the time I'm using on my business, and working at home. He does get to choose where he'd rather sleep - the crib or his bed. If he chooses his bed, which believe it or not he only does about 1/4 of the time, he knows he has to stay in his room and sleep.
He was really fighting his nap breifly right after the baby was born. I put my DD's radio in his room with some soothing music. He loved it so much, but he still fought his nap until I told him the music seemed to be keeping him awake so I was going to have to turn it off so he could sleep. I never have to fight him now, after one time of doing this. I don't consider this a punishment and I don't threaten him, I think it's really a fact that if it doesn't help him fall asleep then it's not working. So yeah... I'm very distracted right now (as usual), but music. That's been the key to getting him to sleep. That and routine.