I had this problem with both Virtual Box 3.3 and 4.0 on Windows 7. While installing or uninstalling, it hangs and I can't even close the installer from the task manager: the only remedy was to hard-reset my computer... blarg...
It turned out to be Virtual Box is doing something with my network connection. Not sure what it is exactly, but I found an easy solution:
- Disconnect your LAN cable from the back of your system
- Install or uninstall VirtualBox
- Plug back in your LAN cable