"Once again, Microsoft thinks it can solve all of your problems by being smarter than you are. Unfortunately, some of the "automatic tuning" features of Vista can yield in lower performance.

One of Vista's features tries to change the network's receive window on -the-fly to adapt to changing network conditions. If you've been experiencing lower network throughput when transferring large files or experience weird network disconnects, then you can try disabling Vista's auto-tuning network feature."