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>