From the AMD FAQ on this processor :
13. Does the Am5x86-133 support Pentium Code?
The Am5x86-133 is a high performance 486, 32 bit processor achieving performance results equal to a Pentium 75. Applications that require Pentium instruction will not run on a 486.
Looking through Winamp's FAQ I get :
What are Winamp's system requirements?
A fast 486 or (optimally) a Pentium or better, running Windows 95, 98, 2000, or NT 4. Or, perhaps, WINE under XWindows. :)
.... so it SHOULD be okay decoding MP3s (just).