this speed tweak worked much better pre-Vista operating systems, as they were optimized for phone modem rather then network connections by default. You would see a huge increase in bandwidth back then. Vista is optimized for network connections already. The other factor to consider here is that you can change the maximum transmission unit (MaxMTU) all you want, but is your service provider has it set lower then your setting, you will see no gain. To get more speed these days you need to figure out what your isp has for settings, and work from that. Most people do this by trial and error, changing one setting at a time, and speed testing after a restart.
Your best bet for increasing speeds is to go to a site like
SpeedGuide.net :: The Broadband Guide and read the faqs.
How To Increase Download Speeds By 100-200 Kbsec
