I've managed to get access to a Spartan6 150 FPGA board and Xilinx toolset at work at lunch/evenings to play with. The idea is to learn VHDL, which is going OK. I'd really like to have a play with Bitcoin too.
I think most of the people worked on the Verilog version, not the VHDL one. I wouldn't be surprised if the VHDL version never implemented correctly on Spartan chips, but maybe on Virtex-es only.
Start your play with the versions that have a top-level ISE project file: *.xise.
Are you trying to learn VHDL knowing Verilog or from scratch?