Tried everything you said to the T and it's still not working.
Not sure why thats saying not digitally signed, I just downloaded from here,
Download Webcam & Headset Software
Checked the properties, digital signature tab, details button,
Everything checks out there.
Are you saving the file to your computer? I always save the download, right click, properties, then click the unblock button, apply, OK.
Then right click, run as admin to install, that might help.
Just curious, do you have service pack 1 installed?
I was getting a message like that for my USB host controller after SP1, found this solution for it,
Win7 SP1 - "Standard Enhanced PCI to USB Host Controller" - Microsoft Answers
After uninstalling, it automatically reinstalled and the issue was fixed.