Well, I have not tried to install IE7, but WinpkFilter x64 build is based on the standard NDIS Intermediate driver (after Patch Guard was introduced making a NDIS hooking solution is possible but very difficult to support) and it is installed through the documented system mechanism.
If MS decided to reconfigure the network on some way during IE7 installation what involves reinstalling NDIS IM drivers (and probably some other network drivers) then I don’t think we can do anything about it except signing driver with WHQL or disabling unsigned drivers policy (as far as I understand you got “unsigned driver warning”, otherwise system would reinstall it without asking you).