The latest revision of virt-manager comes with improved support for SPICE enabled guests. In previous releases, this has been unstable as it was still in development. Although virt-manager added support prior to this latest revision, there had been changes made to the spice related command line arguments of qemu which caused this feature to break. If you run fedora 14 and subscribe to the virt-preview repository you should find that SPICE enabled guests works. What’s also nice is that spice-gtk is integrated in virt-manager so you can view your SPICE enabled guests from within virt-manager.
In order to use SPICE with your guests in virt-manager you simply need to select the SPICE server as your graphics system and qxl video driver as shown int the screenshots below. Of course, you'll also have to install the SPICE drivers on your guests as well.
Selecting the spice graphics subsystem in virt-manager
Selecting your guest qxl video driver in virt-manager
Give it a try and see how it works for you. You'll find now that sound and graphics work really well so you can watch videos now on your windows spice enabled guests.