1) The Vista tweaks are here:
http://www.cableforum.co.uk/board/12...aks-speed.html
2) Sorry, mileage will vary depending on previous settings and current hardware used. Some of these tweaks affect TCP/IP transfer efficiency, whilst some rely on networking hardware in the LAN card to offload some of the processing from the CPU, one even allows compatable hardware to directly address CPU cache memory to avoid bottlenecks. Basically, if there are no problems indicated from the test site and you have a normal home broadband connection then these settings are going to squeeze the last bit out of your connection. If your settings are normal it will be that little bit better. If your settings have been knocked out of whack (common with Vista) then this can seriously boost your speed. The following two lines are the most essential for raw transfer speed:
netsh int tcp set global autotuninglevel=normal
netsh int tcp set global congestionprovider=ctcp
These tweaks can be seen in the same light as the DrTCP tweaks for older OSs. You can get anything from a little top end fine tuning speed improvment to radical improvment.
3) No, the Microsoft compatability test will not blow up your router. The worst concievable result is the need to reboot the router, and if you do need that then the router is awful and should be replaced with a half way decent one. The WGR614v9 (latest Netgear firmware, can't speak as to Virgin firmware) passes perfectly. Still, do the test in case your PC/LAN card/summat else has an issue.