When you try to join the computer to a domain during the min-Setup portion of Sysprep, you receive:
You have entered an invalid password. Would you like to proceed for now and try joining a domain later?
NOTE: The computer may join the domain after the restart and completion of mini-Setup.
The error is generally the result of a network adapter driver problem on the Windows media. Get an updated driver for your NIC.
NOTE: You can use netdom, from the Support Tools, in a script, to join the domain:
netdom join <ComputerName> /domain:<DomainName> /userd:<UserName> /passwordd:<UserNamePassword>