I don’t know what this is all about, but HyperV (at least the 2008R2 flavour) can make it difficult to set up a server 2003 guest, despite apprently allowing all flavours of Server 2003.
What was happening to me is that there was simply no networking, and you couldn’t install the MS version of VMWare tools because it brought up an error complaining that the guest wasn’t supported.
Take the guest down, add a legacy network adapter, then boot up. You should then have two network adapters- one that works and one that brings up the familiar yellow question mark. However at this point you can install "Integration Services", which picks up the faulty NIC, which means you can down the guest, remove the legacy NIC, reboot and have the network functionality you expected in the first place.
(and if you’re wondering why I’m making a 2003 guest, it’s to run a legacy app that hasn’t been tested against any flavour of 2008)