Can't make virtio block driver work on Windows 2003

[Asdo <asdo@shiftmail.org>]

Hi all
I have a new installation of Windows 2003 SBS server 32bit which I 
installed using IDE disk.
KVM version is QEMU PC emulator version 0.10.50 (qemu-kvm-devel-86) 
compiled by myself on kernel 2.6.28-11-server.

I have already moved networking from e1000 to virtio (e1000 was 
performing very sluggishly btw, probably was losing many packets, virtio 
seems to work)

Now I want to move the disk to virtio...

This is complex so I thought that first I wanted to see virtio installed 
and working on another drive.
So I tried adding another drive, a virtio one, (a new 100MB file at host 
side) to the virtual machine and rebooting.

A first problem is that Windows does not detect the new device upon boot 
or Add Hardware scan.

Here is the kvm commandline (it's complex because it comes from libvirt):

/usr/local/kvm/bin/qemu-system-x86_64 -S -M pc -m 4096-smp 4 -name 
winserv2 -uuid xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx -monitor pty -boot c 
-drive 
file=/virtual_machines/kvm/nfsimport/winserv2.raw,if=ide,index=0,boot=on 
-drive file=/virtual_machines/kvm/nfsimport/zerofile,if=virtio,index=1 
-net nic,macaddr=xx:xx:xx:xx:xx:xx,vlan=0,model=virtio -net 
tap,fd=25,vlan=0 -serial none -parallel none -usb -vnc 127.0.0.1:4

Even if Windows couldn't detect the new device I tried to install the 
driver anyway. On Add Hardware I go through to --> SCSI and RAID 
controllers --> Have Disk .. and point it to the location of viostor 
files (windows 2003 x86) downloaded from:

  http://www.linux-kvm.org/page/WindowsGuestDrivers/Download_Drivers
  http://people.redhat.com/~yvugenfi/24.09.2009/viostor.zip

Windows does install the driver, however at the end it says:

  The software for this device is now installed, but may not work 
correctly.
  This device cannot start. (Code 10)

and the new device gets flagged with a yellow exclamation mark in Device 
Manager.

I don't know if it's the same reason as before, that the device is not 
detected so the driver cannot work, or another reason.

Any idea?

Thanks for your help