Download file or copy file are the way to go. Confirm rights on the share and consideration will need to be taken if the machine is in WinPE or in the OS connected to the domain when you attempt the file transfer.
In the Download file Provisioning task, What format is the Source Path expected?
I tried http://myserver.domain.local/SoftwareDistribution/test.zip but it fails, the only code I get is a provisioning action failed Error 1163.
If I create a software distribution task, it runs just fine, the zip is in the same folder.
I'm out of ideas here.