It's annoying and poorly documented but it now seems necessary to use "tap:aio" instead of "file".
i.e. for your example:
disk = [ 'tap:aio:/images/win2k3disk.img,ioemu:hda,w', 'tap:aio:/images/win2k3iso.img,ioemu:hdc:cdrom,r']
This should work.
It's annoying and poorly documented but it now seems necessary to use "tap:aio" instead of "file".
i.e. for your example:
disk = [ 'tap:aio: /images/ win2k3disk. img,ioemu: hda,w', /images/ win2k3iso. img,ioemu: hdc:cdrom, r']
'tap:aio:
This should work.