Replication of Server

Hi All,

I have one Server windows 2003 as a PDC,
also having additional domain & child domain.

I will going to join windows 2008 64 bit server as a ADC.

for that I have to run Adprep.exe on windows 2003 server PDC.

my question is if i m running this exe on server & after this I will get any error on server, then how can i roll back it? & there is any other option to replication whole server with data?

Please give me any suggetion on same.
Thanks