Was able to verify that my Pentium MMX 144 can do VCD, Cinepack, and Smacker (surprising no one.)
I'm about to test the VCD, Cinepack and Smacker files on my 75 mHz Pentium, and then I'll try an xvid file on the pentium MMX.
At some point, I'll try the smacker files on my 486DX66, and see if that's an avenue worth pursing.
Not enough data to draw conclusions yet.