Are you seeing surrounding content in the temporary spot you're looking (the other stuff the page renders, like GIF's, .JS's, etc.) successfully? I'm wondering if you're looking in the right place since Windows 7 has altered the location of temporary files. Check this out (the first user comment is helpful too).
If you're already in the correct spot, you might double-check that your Windows Explorer (not Internet Explorer) settings do not hide files (all those Windows key-E, Tools, Folder Options, View tab settings around "Show hidden files and folders", "Hide protected system files", "Hide known type file extensions" or whatever all those options are - just crawl through here and change the relevant settings, on the root of where your temp is) or you could try a third-party explorer application (like Total Commander) that truly shows everything in a folder.
Lastly, I know your technique is a tried-and-true one to save these videos, and I remember it well, but I might recommend browser plug-ins that do this kind of dirty work for you directly by letting you snag the temporary file or the true file from source. Stuff like DownThemAll. HiDownload can do that and includes a "sniffer" too for locations that aren't obvious showing every file being accessed; you can then feed that to HiDownload itself or something like FreeDownloadManager (which itself now has Flash download capability). Some people like RealPlayer (gah!) still since its "Save" functionality they find robust. Just a standard reminder that whenever you do this kind of thing or use those tools it should be for sites/videos that permit you to save it offline.