Pd-0.38.4-extended was compiled with these flags:

-mcpu=i586 -mtune=pentium3 -O3 -funroll-loops -fomit-frame-pointer

That should work with AMD CPUs, right?

The Pentium3 was the first CPU to have SSE so that flag quite possibly allows the compiler to issue SSE instructions. The original AMD Athlon (and all AMD chips before it) do not support SSE.