There is no QuickTime X version of flip4mac right now so if you want to view Windows Media content, you will have to install QT7 from the SL disc and then install the current version of flip4mac.
There is however, a new Flip4Mac beta that works with QuickTime X which is installed by default in Snow Leopard. (QuickTime 7 is an optional install for SL).
Download Link.
Regards.