I also did the same research as you, but I found that version 5 HAS
been ported to Linux. I downloaded the rv50_linux file and got it
to run on my 2.2.6-STABLE using linux_lib. Only bummer was that I
could not hear any sound... i.e. the player's little marker wasn't
moving accross the horizontal bar.
Any reason why this was happening.. I have a cheap ASOUND btw.
real player 5.0 for linux works correctly on my laptop running -current.
In fact, mtv, xanim, and real player 5.0 are all working fine for
both video and audio.