QuickCam 4000 shows up as “Unknown device” in Windows 7 Device Manager
(USB\VID_046D&PID_08B2)

Download the 64-bit driver from Logitech
ftp://ftp.logitech.com/pub/techsupport/quickcam/qc1051enu_x64.exe

Unpack this .exe file to a folder using 7zip, WinRAR, etc.

In Device Manager right click the device, update driver, Browse my computer and point it to this folder containing the unpacked files.