Preparing SBS2003 for ADPREP.exe

I've been doing some research concerning adding a second domain controller to an SBS2003 domain. I want to make a Server 2003 R2 Standard Ed server a secondary controller. Many people have suggested to run the ADPREP.exe command from the server2003 OS CD on the SBS2003 server. Although it seems like a simple enough procedure, I am hesitant on doing so thinking that something may go completely wrong and corrupt the Active Directory on the SBS2003 machine leaving me with nothing. Is there anything I need to worry about? I do full PC backups using Symantec's Backup Exec every day. Should I really be worried? Has anyone had any problems with this? Thanks in advance.