The variable that should be used to resolve the computer name through provisioning is ldHostname. This is a default variable that is created with the provisioning code and by default is tied to the Device Name of the machine. You can see the default variables in the console. Select the provisioning section of the tree in the OS Deployment section of the console. This will light up the provisioning related icons on the toolbar. Locate the one labeled "public varibales affecting the functioning of the template" and select it. This will show the variables, what they are configured to, and allow you to modify/create variables. One thing that I would recommend, is that you modify the existing ldHostname variable to point to "Computer"."Display Name" instead of Device name. This is due to the information reported with a miniscan.
No matter what, if a machine is running a provisioning job, then it will have some kind of record in the LANDesk inventory. By default, when a machine PXE boots and launches into PE, it will send a miniscan to the core server and report the device name as the mac address. If you want to specify an actual machine name to use, then you would want to use the bare metal or csv import function to add the machine to the inventory ahead of time.
Keep in mind that the variables are case sensitive. Additionally, I would recommend you check out the following sample templates:
The image deploy script contains a sysprep.inf with the provisioning variable for computername already added.
Hope this helps.