Question on Replication

Hi,
I just went through the install notes on erserver1.2 and saw a mention 
in there that every table for replication requires a integer based 
column. It also states that a new column is added for every table that 
is replicated.

The tables I intend to replicate already have such a column. Can the 
server be configured to use these instead so that the tables on both 
server remain unchanged ?

What is the overhead in using replication and what is the timing of the 
replication. I have a database and we add roughly 100k records during an 
update operation.

I did not find a lot of information on that except 2 small documents in 
distribution. can anyone point me to the site where there is a detailed 
description?

Thanks
Alex