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#11
If this moves the Active System partition to Z as desired, then you can delete the C; partition and use a 3rd party partition manager like Partition Wizard to recover the space from deleted C: into your Z partition.
The easiest way to do this, after making sure Z: is now set as active, is to boot into Partition Wizard, right click on C: and delete, then right click on Z: choose Resize/Move then just slide the left border of Z over the deleted C space to encompass it all.
There is the slight possibility you will have to run Startup Repair from the Installer disk's Repair console.
Suggest before doing anything you type Backup in the Win7 start box, then Create an Image of your HDD to save to your external so you can easily reimage the HDD if you need to start over, since moving operations can fail.