If you're interested in turning off FreeType hinting, search for the following line in the gd source (gdft.c):
err = FT_Load_Glyph (face, glyph_index, FT_LOAD_DEFAULT);
and replace it with
err = FT_Load_Glyph (face, glyph_index, FT_LOAD_NO_HINTING);
Recompile GD, and vo?la: beauteous antialiasing.