>It's hard for me to beleive that at this point the
>Losties could actually be one up on the others, you
Maybe there is a way for Henry not to be one of the Others. Could he have been a "small time worker-bee" in one of the abandoned hatches? I get the feeling there's a difference between the Others and the hatch attendants (such as Desmond.was). The Others are running the Dharma Initiative experiment from the looks of it (bad guys), the attendants are just the guinea pigs or lab workers (aka computer attendees) in the experiment making them neutral or not-so-bad guys. To me, they seem to be on two different sides. If Henry was only the hatch attendant or worker-bee, he wouldn't really be one of the Others the way he sees himself.
Whoever drew the map on the hatch door obviously had time to explore the island. Didn't Desmond say there were 2 people in the Losties' hatch originally (Desmond and somebody else)? One could have stayed to do the numbers, one explored. Assume that Henry was assigned to another hatch, he and his hatchmate took turns doing number duty and exploring. If the hatchmate stumbled on the balloon, found the real Henry dead, he could have buried him and told our fake Henry about it. Hatchmate would have had a chance to find the ID but probably didn't bother mentioning the race (or our fake Henry knew but didn't think the Losties would have what it takes to dig up a body and find out the truth). He wasn't planning on getting caught, so on short notice he decided to use the balloon crash story, knowing there was some evidence there to back him up if need be.
For all we know, Desmond is still on the island. Danielle probably hasn't seen him, might not even know he exists. If she were to catch him, she'd assume he's one of the Others. She caught our fake Henry instead and assumed he's one of the Others since she hadn't seen him with the Losties.
Again, assuming the fake Henry has experience in a hatch, he'd know how important it is to enter the numbers on time. It could explain why he didn't try to escape and why he remembered the numbers correctly. Either the sequence was the same as what he had to enter, or he made darn sure he got them right because there'd be no time for a second try at it.
In the preview he's being interrogated about what he knows about the Others. He might not know much, but he would certainly have picked up some info that he could reveal under duress. He probably also knows enough about the Others to not want to be turned loose and get picked off by them.
Right now he's between a rock and a hard place. Either reveal he was working in a hatch, possibly spilling secrets that he knows the Dharma Initiative doesn't want revealed, or he claims to be an Other and suffer the wrath of the Losties (specially Sayid who's itching to get even about Shannon's death).
Maybe somebody will think of asking Henry the Snowman question, see if he answers it? If he really is an outsider who crashed on the island, he wouldn't know the answer or wouldn't react suspiciously.