On reading your mail, i have the same doubt.

1) I have not seen any instances of locking a
table/database/row in any of the ADO.Net examples i
have seen so far.

2) In a disconnected dataset environment, how does the
system take into account the changes that might have
been made by another user, before this dataset updates
back the database ?

It appears that locks in ADO.Net are implemented by
the isolationLevel associated with the ADO.NET
Transaction. I suppose that by default it is
"ReadCommitted" which would be some kind of a
pessimistic lock.

I hope somebody can confirm or correct this.