If you’re installing Hyper-V Server 2008 (the free stripped down OS with Hyper-V) then make sure you have configured DEP and CPU virtualisation assistance in the BIOS beforehand. The OS will install and setup the Hyper-V role even if you haven’t configured the server hardware. Obviously Hyper-V won’t work without these being configured.
And one thing is missing from the configuration menu: the firewall. I’ve set up a machine for some lab work and remote admin via the Hyper-V console proved impossible until I reconfigured the Windows Firewall on the Hyper-V server.
I installed the VMM 2008 agent successfully. The "update available" issue sprang up immediately. Installing KB956589 and KB956774 on the Hyper-V server fixed that (reboot required). That wasn’t much of a problem because I’ve previously encountered it. I wonder if you can build a WDS image from the Hyper-V Server media and stream these updates? Whenever I have free time (2011 by the looks of it) I’ll have a look.