All three of my daughters have gone through night terrors, so I've done a fair amount of reading about them. With a night terror, the child usually appears awake (eyes open), but is really sort of stuck in one of the normal wake/sleep transitions that happens normally throughout the night. Usually they happen in the first three hours of sleep, and often they involve intense screaming, and frequently thrashing/kicking, etc. They may look right at you, but don't really see you. They do not remember them in the morning. (Just for comparisons, nightmares usually happen later in the night, the child is more asleep, and they often remember after waking or the next day.)
In many cases, night terrors are caused be a child being overtired. I know with all of my girls we saw/see the most night terrors when they go from 2 naps to 1 and when they give up napping all together. So you do want to make sure your son is getting as much sleep (and on a regular schedule) as he needs. Obviously there will be times like the nap transitions or illness where you can't help them getting a little overtired, but just do your best.
It seems that what works best depends on the child, but you do not want to wake them. It seems from the other responses that some kids do like to be held, but that always seemed to freak mine out more (again, unlike with nightmares). One of mine would respond well to you calming and quietly repeating, "It's OK, it's OK" over and over. For the others we sometimes just had/have to put them on the carpet so they didn't get hurt with the thrashing around. With one of mine, while I didn't physically wake her, when she would start winding down I would calmly say, "(her name), mommy needs you to wake up now" and that would sometimes help her come to. Generally the stop very suddenly, and then you can just tuck them back in and they go soundly to sleep.
For what it's worth, I do not think the time your son cried right when you put him in the crib was a night terror - more likely related to the cold or a possible ear infection, so I would check with the doc if that continues. A good book for sleep reference is Jodi Mindell's "Sleeping Through the Night" - it does have a sleep training component, which you may or may not agree with, but it also has some really good info to help understand sleep and sleep problems more.
Good luck!