[libvirt-users] getting oriented/networking

I've been using virt-manager and kvm with a disk image (as in the raw bits) from a physical windows 7 machine. Initial performance was dreadful, but improved as I switched to virtio and spice. I've been running linux VM's somewhat longer (much longer if you count kvm without libvirt). There are lots of choices exposed by virt-manager. How do I find out what the choices mean, and which are good ones? This was true for the video (resolved by following instructions for spice, though I still wonder what the other settings are for), disks and the network. In particular, I have a choice of lots of interfaces for my network; I picked eth1:macvtap because I wanted to bridge eth1. But there is a "Source Mode" which I left at VEPA, even though Bridged was another choice. But the bridge would already seem implicit in picking a source device of eth1:macvtap. I don't know what "source mode" means. The choices in the GUI seem like some of the options listed under forward on http://libvirt.org/formatnetwork.html; is that a good place to look for clarification. I started a 2nd VM that also used eth1:macvtap (with virtio) and it had almost no network throughput. So maybe I should use some other method? I notice the network manager connection gui allows creation of bridges on the network; should I be using that? I have been reading documentation, but I haven't found either a task-oriented discussion ("to get a windows machine working well, use these options" or "follow these steps") or an easy way to go from the choices in the GUI to a discussion of their meaning. Thanks for any help you can offer. Ross Boylan