Try using Process Monitor (not Process Explorer) from Sysinternals. It's a bit of an unwieldy utility, but if you set up a filter for the installer (or maybe for the path in question, either ought to work) and then reproduce your issue, maybe you can see why it fails to open it as it ought to display the reason for the failure. I find it hard to believe it is a problem everyone running Windows 7 has as most packet-inspection utilities lean heavily on WinPcap.
Alternatively, try installing another program that comes with Winpcap? I seem to recall software bundling it with their apps to make them easier to use. An example of such a program would be Nmap. (It's kind of a hack, but probably easier than debugging the problem like I suggested just now since it wouldn't garantuee a fix...)