In MDT 2012 Update 1, if the “JoinDomain” rule is specified then the Capture Wizard screen is not displayed. Also, the Capture Image screen appears even when Deploying an image. You can workaround both of these issues by creating a new section in your CustomSettings.INI for WinPE.
[Settings]
Priority=OSVersion, Default
Properties=MyCustomProperty
[WinPE]
SkipCapture=YES
DoCapture=NO
JoinDomain=mydomain.com
[Default]
OSInstall=Y
SkipCapture=NO
SkipAdminPassword=YES
SkipProductKey=YES
SkipComputerBackup=NO
SkipBitLocker=NO
/Brian G