Now, up in the Menubar, go to Window -> Activity (or hit Alt+Command+A)
Now, you will see all your tabs there, each one has its own grouping. Find the tab with the video in it, let the page fully load, and then, double click the item that is the largest.
This will open a new Safari window and then force a download. Once the download is complete, add the extension .flv to the end of the file name. This is now playable in VLC, or Quicktime (for best results under quicktime, and in the eventuality that it does not immediately play, download Perian, which you should have done anyway, cuz it is AWESOME!)