When installing a new domU, xenguest-install.py should be able to format a xen config file that supports multiple NICs and multiple disks. Attached is a version that does just that.
Created attachment 126329 [details] xenguest-install.py that supports the requested features
xenguest-install has been rewritten a bit and the backend code definitely supports multiple disks/nics now. The difficult part is how to handle it via the command line; asking for more than one in the asking questions form of xenguest-install is going to be very error-prone.
In FC6 and later, xenguest-install.py is replaced by the python-virtinst RPM. The 0.98.0-1.fc6 release of python-virtinst contains support for multiple nics / disks. There are no plans to add this in FC5 or earlier because they used the legacy xenguest-install.py script.