Here are your best options for getting a Windows XP qcow2 image for use with QEMU/KVM (including Proxmox, virt-manager, or CLI):
qemu-img convert -O qcow2 source_disk.vmdk windows_xp.qcow2
Explanation:
Attach a secondary, dummy VirtIO disk and a dummy VirtIO network card to the VM. windows xp qcow2