Try this out and trust me you WON'T be disappointed.
Get DOSBox 0.72 and in the config specify cylces=max and core=dynamic.
I'm on P4 Core2Duo 2.66 ghz, 2 gigs ram and e-VGA nVidia GeForce 8800 GTX --
-- and I'm getting an avg. frame rate of 300 FPS.In any case, on a crappy 1.8 ghz with 128 mbs ram machine you should get around 60 FPS like a champ!