First you connect your M-Audio soundcard to your PC via USB, and the monitors to the soundcard's "out"s. Take the time to set up everything properly so that your computer does recognize the soundcard as your primary sound device, else the rest just won't work... Then you can either plug the mic directly to the soundcard (if it has phantom power) or to the mixer, then plug the mixer's "out"s to the soundcard's "in"s (it is likely that you will get better results with the mixer but if the MobilePre features phantom power you can try both solutions just to see... well,
hear ;) which combination provides the result which suits you best).
Also, from your question I suppose that you don't yet have the cables, do you? so PLEASE, DON'T go for the cheapest cables as there IS a REAL quality difference between a 5$/5€ cable and a 15€/$ one. Of course you don't need 150€ cables for recording in a home studio, but the cheapest ones available on the market will totally "narrow" your sound, you will lose a lot of clarity in the signal and may get really disappointed by the result -- not because of your mic or soundcard, but just because of the cables...