Very slow performance Solution: Enable KVM acceleration ( -accel kvm ), add -cpu host , increase RAM, use VirtIO block driver.
qemu-img convert -f vdi -O qcow2 windows7.vdi windows7.qcow2 Or from .vmdk : Download Windows 7 Qcow2 Image Free
No network Solution: Change NIC model from e1000 to rtl8139 or virtio-net-pci . Very slow performance Solution: Enable KVM acceleration (