Constant issues connecting Hyper-V virtual machines to network

I've set up at least a dozen virtual machines, and I always have problems connecting them to my external network. Guides always make it look so easy... There has to be something that I'm missing.

System configuration:

Host: WS2k8R2 Standard ─┬───────────► Hyper-V ────────► VM: WS2k8R2 Standard
                        │                                 ▲
                        └► Hardware NIC ──► Virtual NIC ──┘

EDIT: I like diagrams. ☺