If you have an older router, Vista’s network auto tuning feature will cause it to get confused. Some suggest turning off Stateful Packet Inspection (or SPI) on the router will fix the issue. Others say updating the firmware will work. If your router does not have an option to turn off SPI or you do not want to do so, or if your router manufacturer no longer provides firmware updates, the last option is to turn off autotuning.
Here’s the magic command line to do so:
I recently rebuilt a laptop and had a hard time finding this solution again. Now it’s documented in a well known place for me (and you as well).