esmail9 wrote:When I'm downloading packages/upgrades for Ubuntu in the VB, the network connection is quite speedy first, but then slows down dramatically, until I only get a about 60 kB/s .. my download speeds under XP are much faster, as they are when I boot into a native Ubuntu partition.
NAT has always been slow IIRC. It is possible the "faster" speeds you are seeing are an illusion.
When the "what do you want to do with this file" dialog pops up in some apps, the file is downloading in the background while you decide. Let's say you actually have a constant 60kb/s (it won't go faster) and you sit at the dialog for 5 seconds before dismissing it and causing the actual download meter pops up. If the app does not properly compensate for those 5 seconds, the download meter may erroneously believe 300kb has been instantly downloaded and show a 360kb/s download rate after 1 second, and then 210kb/s next second (since it's averaging 420kb over 2 seconds instead of the correct 7). The real download rate is still a steady 60kb/s. You can usually recognize these apps by the download spike at the very beginning that quickly drops (like you describe) but it will happen again if you start a new download.
I don't know if Ubuntu is guilty of this or not, but you can determine it easily.
Install one package, then exit the package manager, then start it up again and download another package. If you get the same download spike, there's no way IMO the network interface itself can have those weird download spikes since VirtualBox doesn't know or care about high-level protocols or connections (at least, AFAIK) so all packets would be treated the same. If your NAT connection slows down it should not speed back up for a second package download since it doesn't know or care when that happens, it just sees raw data.
I recommend using the Host Interface networking instead of NAT. The only reason I can think of using NAT instead would be for security purposes to keep others on the network from poking at your VMs, but Linux really isn't as much of a target for that sort of thing as Windows, and with a properly configured network (and guest OS) there really should be no issues.