Well so far in my course I've found that even if you find dissection cadavers gruesome at first, you get used to it. I remember the first time I was in the dissecting room, I was quite nervous and was nauseous as well, so I just mostly watched whilst the other keen-beans did the dissecting, but after seeing it done, touching the cadaver and seeing that it actually feels nothing like a real person, it's not too bad - they don't bleed when you cut them, so it feels almost as if you're cutting through a model rather than a real person, but I guess it'll be different in surgery.
Prosection sessions also help, this is where you examine like arms and stuff which have been pre-disected and are no longer connected to the body - I think that by holding, analysing and playing with these dissected parts, you kind of get used to the whole notion of dissecting cadavers. It's because when they are detached, the arms and other parts don't feel like they're a part of the person (if that makes sense).
Anyways, if you don't feel comfortable cutting and working with cadavers early on, there will always be keen ones in your group who want to start off, so you can just watch for the first few sessions before digging in, but of course, you learn more if you actually get your hands dirty.
I agree with Shinny though, the emotional side of things is probably more confronting than the actual cadaver dissections. But I haven't been in that situation yet.
In all honesty though (and I'm sure pi would agree here

) the thing I've found most confronting is the...workload

heheh
Moderator action: removed real name, sorry for the inconvenience