Windows Vista has a self tuned RWIN, and it works fine, Microsoft hasn't realeased much info about specific TCP registry keys yet, but i been testing some of the keys from windows XP. Turned out the DefaultSendWindow also works with Vista.
The things you need to do if you have Vista and cant reach 90% of advertised speed, beside the points in this sticky is
1. Make sure TCP autotuning is enabled, go to start-run paste this " netsh int tcp set global autotuninglevel=normal " and hit enter.
2. Download and install Cablenut cablenut408.zip
3. Disable UAC, go to start-run and type msconfig, click on tools tab and scroll down to "disable UAC" click on it and then click Launch. Reboot your PC.
3. Download and unzip this uploadtweak VanBurens_cablenut_settings_all_versions.zip , just click on the ccs file and click save to registry in adjuster, If cablenut ask for a OS when your trying to apply the settings, use Windows 2000.
4. Reboot your PC
5. Test speed again