My setup:
Server:
- HP Proliant DL140 G3
- Intel Xeon 5160 (Dual-core 3 GHz)
- 9 GB RAM
- 2x 73 GB SAS drive in RAID1 (hardware RAID)
- Dual 1 GB/s NIC
- Windows Server 2008 x64 Standard
(At first I had only 5 GB RAM, but I ran short and I installed another 4 GB.)
VMs:
- Windows 2003 Server (x86) with 512 MB for DC, GC, DNS, DHCP
- Windows 2008 Server (x64) with 1 GB for WSUS 3.0 SP1 x64
- Windows XP Pro (x86) with 512 MB for FTP server (Serv-U) and Sybase Anywhere server
- Windows 2003 Server (x86) with 2 GB for Symantec Endpoint Protection Manager (SEPM)
I also installed CA ARCserve 12.0 on the host OS. The server uses about 5.6 GB RAM (out of 9) and CPU utilization is low.
My conclusion: Hyper-V is ready for prime time even though in beta. Don't forget that you need a NIC for management so at least 2 NICs are required. (I'd like to have 3 to connect one to the DMZ but my server doesn't have a free slot because of the SAS adapter for the tape backup.)
Also do not cut on RAM, you need to add up the RAM allocated for all VMs, the host OS and any apps on the host.