I read a anand review on it a while back. It sait it performed within 1-2% of all the other MX cards they tested. In 16 bit color, it runs good. In 32 bit color it takes a huge hit (as does all MX cards).
Make sure it is either the origonal MX card or the 'new' MX 400. The MX 200 is a step below a TNT2 Ultra in performance.