Yeah, you are right I checked things last night, did some googling and it seems that 6 SPE's are available to linux... the second processor is somewhat "emulated"
.. anyway:
Here is something nice: http://code.google.com/p/cell-mpeg2-decoder/
MPEG2 Decoder optimized for Cell BE/PS3, it plays streams up to 720p at 30fps.
I didn't tested it but someone over at YDL boards certainly will and make it available trough a RPM... Can't wait!