What Havok forgot to mention is that Mr Do's instructions don't include how to compile a 64 bit version of Mame so his advice won't actually help you. Mame Compiler cannot compile a 64-bit version of Mame because the GCC compiler can't do it (yet) which I've mentioned several times before in this thread.
Huh? Where? I only see one post...
Anyways - thanks for the heads up about 64 bit compiling, I'm sure GCC will happen soon, as 64 bit is mainstream now...
I have no plans on support for 64-bit versions of Mame Compiler until a working makefile support for MinGW 64. The simple solution for now is take the AMD optimization setting off in Mame Compiler or follow Mr Do's instructions (without adding the AMD64=1 setting) if you still have the inclination to "build character" 
Character is good, and knowledge is power.
Nice tool by the way, and I mean that in a non gay way...
