I found it possible to playback Flash video, the one with FLV1 as the FOURCC, in Windows Media Player and even in Premiere Elements.
First you need an FLV Splitter. You can download that from http://sourceforge.net/project/showfile ... _id=205650. The one you want is named FLVSplitter_20080127.zip. After downloading, you unzip it, then you have to register the .ax file using REGSVR32. You can do that by going Start > Run and then typing REGSVR32 "C:\your download folder\FLVSplitter.ax". Alternatively, if you have the Windows Essential Codec Pack, that has the FLV Splitter under the Containers category when you install it. The .ax will be registered automatically. You get the WECP from http://www.mediacodec.org/.
Then you need the FFDShow package. http://sourceforge.net/project/showfile ... _id=173941. You want the latest stable generic beta release, ffdshow_beta5_rev2033_20080705_clsid.exe. After installation you need to go Start > All Programs > ffdshow > Audio Decoder Configuration, then enable MP3. To enable the Flash codec you go Start > All Programs > ffdshow > Video Decoder Configuration, and enable FLV1.
Now you should be able to play back FLV files in Windows Media Player 11, and import FLV files into Premiere Elements 4.0. Premiere Elements uses it own MP3 decoder, but Windows Media Player will use the one enabled in FFDShow. If you check the OSD option in FFDShow, information about the file will be displayed during playback. That is useful to check if FFDShow is being used for decoding in Premiere Elements.
Premiere Elements will not import files with the .FLV extension, so just change the .FLV to .AVI.
When installing FFDShow, I accepted the default options on the first screen -- there will be only two items selected. But later when presented with a long list of codecs, I unchecked everything. After that was an inclusion list of applications to use with FFDShow. I checked the option to not exclude any application; there's one screen for audio and one for video.
FFDShow also has a DV codec that you can use instead of using the Panasonic Codec. When selecting which codec to use for compression in VirtualDub, for example, you select FFDShow Video Codec, then click the Configure button, then select DV as the encoder from the dropdown list. You will be using a Video for Windows codec, not a DirectShow codec, FYI.
EDIT (Jan 8, 2009): The link to the FLVSplitter download has been changed and is now linked to the Matroski Splitter, which also works. You do not need to manually register the splitter with Regsvr32. On another note, in addition to enabling FLV1 in FFDShow, you may want to try enabling VP6F (On2) just in case FLV1 doesn't work. Some Flash is h.264. Having a good media info utility to tell you what codecs are in the FLV file can help you match the fourCCs listed in FFDShow.