thanks for the replies so far.
with the souls of those of young age who may not realize being dead or those souls who enter a dead body for example, is that possible? a couple of years ago a hindu member (can't remember who) was saying that once the person dies, the soul moves on to (for lack of a better word) 'heaven' which has different levels of density. doesn't this happen immediately after death without the choice of the soul/person preventing the souls from entering dead bodies or thinking that they are not dead? or is it the soul who chooses when to enter that realm?
Hinduism is vast, as you probably know, so what Andal said is very true. Don't expect the same answer from everyone, regardless of sect. So just because some Hindu at some time said something, it really doesn't mean much. Certainly nothing with any authority.
Here is my view on some of what you ask: A soul cannot re-enter a dead body. There is no heaven or hell in the Islamic or Christian sense. There is an in-between place like the astral plane where souls 'wait' for another birth. As Andal said, the time varies. From my POV, it can be quite a long time, up to 10 years of more, if the soul is 'picky', The ability to determine birth; where, when, etc., depends on the age of the soul and it's desires from the previous birth. The soul will depart the body immediately upon death, but may hover around in a confused state. That's why cremation is done... so the soul does move on.
In my sampradaya, moksha simply means not having to come back, but the absolute conclusion is total and complete merging with God, as water to water. This idea will vary a lot depending on wheter its a pluralistic, dualistic, or monistic school. This is the view of monists.