On my Vista install, I've noticed that BitTorrent downloads are not as fast as they were for me in XP. From what I can gather, this reduction in speed is due to difference in the AutoTuning function that Vista uses on the TCP/IP stack. The optimizer actually results in slower downloads. This affects BitTorrent and other programs that make use of threaded downloads.

If you are seeing slow downloads in BitTorrent too, you can disable the AutoTuning in Vista, this worked for me. To disable the Autotuning, follow these steps.

1. Click on the Start menu and type cmd in the search box. But DO NOT hit Enter after typing cmd. Instead, hold down the Control and Shift keys, and hit Enter while still holding them down. This opens the command prompt with elevated privileges.

2. In the command prompt, type netsh int tcp set global autotuninglevel=disable and then hit enter. It should respond with a line that says Ok.

3. It Windows, so you know naturally need to reboot.

Making this change should speed up your BitTorrent downloads, but if it messes up something else as a result, you can always revert the change by following the same steps but replacing the command in the command prompt with netsh int tcp set global autotuninglevel=normal

Happy downloading!