For anyone who's interested, I just installed QuickTime 6.5 on my Linux box and it plays in SecondLife. My only gripe now is that SL doesn't know how to play nicely with the Linux sound system, and so monopolizes it, but in this case that's WineX's fault.
As an addendum: PLEASE MAKE LINUX CLIENT ABLE TO USE ARTS/ESD/OTHER, DON'T ACCESS SOUND HARDWARE.
