MDT Task Sequence Variable Problem

Hi, 

I am trying to figure out where and when Task Sequence Variables are processed in MDT.  

I have several that are running from the customsettings.ini and I am trying to add some to the task sequence using "Set Task Sequence Variable"  (See list below).  These are intended to modify the Pre-Deployment Screens and settings on a Task sequence by task sequence basis.

DoCapture=YES
SkipComputerName=YES
ComputerName=DIV-CAPTURE
JoinWorkgroup=WORKGROUP
SkipApplications=YES

Where in the Task Sequence should these be set?