> Thanks for your answer Haydn, but I did not understand the issue too.
> Victor has explained my problem clearly, is kvm uncapable of running
> the bridge at 1GBit if it is not a e1000 network card?

Hey Miguel,

what Haydn meant was to force qemu to *emulate* a e1000 NIC instead of the default RTL8139. That emulation is done by qemu in userspace and has absolutely nothing to do with your physical NIC por the bridge.
Chosing a NIC is done with the "model=" parameter.
kvm -net nic,model=e1000

Even better performance-wise would be to use the new virtio interface which paravirtualizes your physical NIC instead of emulating one.
For that, use:
kvm -net nic,model=virtio

Of course you'll need to install the corresponding drivers in your guest. The e1000 should be supported in every guest and for the virtio interface there are windows guest drivers (see the kvm-announce mailing list for that) as well as linux guest drivers included in kernel 2.6.25 upwards.

By the way: This is good stuff f you're interested in hard disk performance, too: http://kvm.qumranet.com/kvmwiki/Virtio

Felix