You install Windows 2003 Hyper-V guest and you can’t install add-ons required to get access to the network because it’s a pre-SP1 Windows OS. You can’t copy/download the SP to the VM because it’s got no network adapters.
Solution 1: the VHD mount script posted here. Shut the VM down, mount the VHD and copy the SP (and whatever you want) to that disk. I used the PowerShell version because it’s shorter and – of course – again got stuck with the unsigned PowerShell script problem. This time, though, I reused the “worst practice” workaround that I wrote about here. Done! To unmount, Save As… and add “un” before “mount” in the last line.
Solution 2: In your Hyper-V manager right-click on your (host) server and select Edit Disk.
So far I’ve been happy with Hyper-V although I’ve unnecessarily wasted too much time trying to get Windows XP x64 going (not supported).