Hi
Mad MP3 decoder lib(
www.mars.org) and mpg123(h**p://www-ti.informatik.uni-tuebingen.de/~hippm/mpg123.html) both uses fixed point math. MAD is very fast. It provides almost the same decoding speed on ARM processors as the decoder provided by ARM Ltd and if you modify a little bit you can reduce the code size to less than half. A simple MP3 player can be buit by using MAD and cirrus logic ARM based controller that has Digital Audio Interface.
If you want to use FPGA, Xilinx freely provides a MP3 decoder source in both Verilog and VHDL. it can be downloaded from thier web site.