AMD X2 4000+ (dual core)
I am running the Win 32 command line of MAME.
Is there a "dual core version" out that is optimized for my processor? Perhaps a command line that I need to initiate somewhere?
Current mame is multithreaded capable, but the increase you might see is around 0%-5%. Enable -multithread (aka -mt).
Also there are athlon and athlon64 optimized builds of mame. You can compile your own, or try to find one out there (I didn't find a current version on my one google try). The increase compared to standard build: 0%-5% or even (but rare) a 0%-2% decrease depending on the game. More common on the net are i686, pp, and pm optimized builds, which might help your cpu but probably not as much, and p4 optimized which might crash your cpu in rare cases.
And if you used a 64 bit build of mame (on a 64 bit OS, of course), you'll see the biggest jump on most games. (A very few games slow down, though.) Either Vista64 or XP64 will run the official mame 64 bit binary.
Good luck