"As it turns out, Windows XP Professional (which this tweak requires, by the way) allocates only 20 percent of the available bandwidth to your internet connection.
Run gpedit.msc and go to Computer Configuration > Administrative Templates > Network > QoS Packet Scheduler and set the Limit Reservable Bandwidth setting to enabled and the limit to 0%. You can squeeze additional download speed from your connection."
I just tested it out, and I didn't see any difference. I did the extremes (0-100%) and still didn't see any change. It is possible that my testing sources were less than perfect, but I'm inclined to agree with Tarun on this one. Oh well, it was a cool idea anyway.