I've installed H2v on various Win 7 systems. Only today did I have an issue with the updates. It seemed to be stuck in an infinite loop, it would repeatedly download my profile and the same update. I am aware there are multiple updates but this was the same one over an over.
The solution was to set the Halo 2 executable and the Launcher to Run as Administrator:
So go to where you installed H2v and right-click the main executable (halo2.exe) then click Properties, then select the Compatibility tab. Check the Run as Administrator box.
Do the same for startup.exe just in case.