OK, thanks. Both of those make sense, but I guess that's why I'm stuck. I don't know how Windows determines the drive letter for a partition, and I don't know where in the unattended configuration I should insert a diskpart script to get it to run at the right time, T-39 as you said. I'd rather do it the diskpart way, if I can, so I have two questions about that. First, where should I insert the script in the configuration to get it to run at the right time? Is cmdlines.txt the right place? It seems like that would run too late, but I'm not sure. Second, I don't understand how to tell diskpart which partition to change the letter of. I guess it will run after the partition and format step of the setup, so windows should already have assigned drive letters to the partitions I created, and I suppose I could do an install without diskpart and just see what drive letters get assigned, then use those in my diskpart script to reassign letters. Would that work? Thanks a lot for your help.