Note: MPlayer 0.90pre8 has been removed as Timo has created a new tardist of Mplayer v0.90rc3 which makes this version obsolete. Please see his comments here for the new download link.
I recently came across a tardist of MPlayer 0.90pre8, a popular multimedia player for Linux (in fact, the official site calls it "Movie Player for LINUX"). It's not the most recent version currently available, but seems to work quite well.
This tardist depends on SDL-1.2.3 from SGI's Freeware site so grab that if haven't already. Until the new IrixDiVX is released this is the best solution for DiVX playback under IRIX. Thanks go out to timo for providing this tardist to the SGI community!