One possible solution: Just wait.
This has always happened to me when updating a Windows machine since Windows 7. Windows 8 does this too.
Basically Windows Update doesn't report progress on downloading (why it has a progress bar for it I have no idea), even though it actually is downloading. This has always been the case for me on multiple machines using both Windows 7 and 8.
At some point it'll jump from 0% to 100%, then begin "Installing", where the progress bar will actually report on percentiles between 0 and 100 as long as you're installing more than one update.
If you have a good connection to the Internet (1MB/s+), and it's taken more than an hour or so, then it's probably actually stuck, but in my experience I've never had to do anything but wait.
Good luck!