Hi
I saw the very same problem today - latest W2k8 Web x64 R2 to be installed
pve running:
pveversion -v
pve-manager: 1.6-2 (pve-manager/1.6/5087)
running kernel: 2.6.32-4-pve
proxmox-ve-2.6.32: 1.6-19
pve-kernel-2.6.32-4-pve: 2.6.32-19
pve-kernel-2.6.18-2-pve: 2.6.18-5
qemu-server: 1.1-18
pve-firmware: 1.0-8
libpve-storage-perl: 1.0-14
vncterm: 0.9-2
vzctl: 3.0.24-1pve4
vzdump: 1.2-7
vzprocps: 2.0.11-1dso2
vzquota: 3.0.11-1
pve-qemu-kvm: 0.12.5-1
ksm-control-daemon: 1.0-4
I see a _big_ performance difference on the virtual server having RAM between 512 MB and 2 GB - the final decision was to go with 1 GB for resources, while performance is acceptable, 512 MB makes even the setup process unbearable.
Also running on 2 GB RAM it never black-screened - but this might be simple coincidence.
Windows-Updates are a big pain anyway as the server-reboot seems always to kill the virtual machine right now - this is not nice - and we have no idea on how to debug this issue.
And for virtio-drivers - I'd kill for some x64 certified virtio-drivers