Does Premiere show an error, it can't read it?
If not an it is Sorenson-made, perhaps Sorenson will and you can convert it with it. They offer a 30-day trial:
Premiere Pro CS5 won't import H.263, more commonly known by the brand name "Sorenson Spark." From File formats supported for import:
Note: Premiere Pro CS5 can import FLV files with video encoded using the On2 VP6 video codec; Premiere Pro CS5 can’t import FLV files with video encoded with the Sorenson Spark video codec. As with any unsupported format, transcode the file to a format that Premiere Pro can import.
You can convert these with FFmpeg, or a GUI called WinFF. Some instructions and options here: Re: Video Converter
I did figure out a way to import these into CS5, but it involves AviSynth and a couple other tools; easier just to convert them directly.
Thanks, Colin! Worked like a charm!