Just downloaded the free version of Hyper-V core. 
available on Microsoft's web site. It's a whopping 1 GB download, but on a 4 MB ADSL it took less than 45 minutes to download, and I got it on the first attempt wow! I installed it on a £500 Intel Duo 2 T7250 CPU laptop (see later). Following Microsoft's "Hyper-V Server 2008 Setup and Configuration Tool Guide" was pretty straight forward. My only trouble was getting the network card going, much the same as when I installed Win2008 full version on the same laptop. I fixed it with a bit of regedit jiggery pokery.
If you are thinking of installing Win2008 (Hyper-V) Core, I strongly recommend installing the full version of Win2008, to see if you have any hardware issues. My laptop had a Via Fast Ethernet NIC, and it had the same problem as the Dell Broadcom Nic "IPv4 Large Send Offload" (see http://hypervoria.com/hyper-v/network-issues-with-windows-server-2008-rdp-and-vs-hyper-v-on-dell-servers.aspx) Installing Win2008 in evaluation mode (using any disk, but not inserting the key) allows 30 days eval. (see http://hypervoria.com/forums/t/136.aspx). With a full install, it is easy to fiddle with configuration such as adjusting the advanced NIC settings, especially disabling TCP Offload (to get the NIC passing data!).
With Core, fiddling with the NIC settings is only possible through the registry (Regedit or Regedt32). The trick with Core, is to check and change the NIC settings directly in the registry (once you've figured out which ones). For me it was LSOv1Pv4 = 0 (and a reboot), to disable "IPv4 Large Send Offload".
Now I just need to find a Vista PC, and install the Hyper-V admin tools!
My "love / hate relationship" with Microsoft, has taken a turn for the better!
I am still unconvinced that Microsoft has taken the the right step with Vista / Win2008, AND Hyper-V, I think the much leaner Win2k3, is a superior product. Vista / Win2008 is muddled, overcomplicated, and bloated, I just hate it. I also fail to see Hyper-V's advantages over Virtual Server 2005; but I guess, working in IT, I have to keep up with the latest offerings.
Well done Microsoft for giving away VM software free, though I do feel some sympathy towards VMware. I really do hope that VMware can keep in front of Microsoft, with competition, we should see some real inovation.