I have no idea where to begin either. You don't give an mp3 demo of sorts, and you don't tell us which version of Reason you have. Please, for your own sake - next time you or anyone else who starts a topic like this:
provide a short mp3 demo of the actual sound - don't let other people do the work of searching for you.
Right now you're restricting your audience to the set of people who 1) still have their factory patches intact, 2) have Reason, 3) have an MS2000 too and 4) time to spare to figure it out for you, which means you will not be likely to get any replies. See?
However, it turns out that Synthmania has a patch here:
http://www.synthmania.com/ms2000.htm and that I have both time to spare and a trial version of Reason 4 so I'll be nice and try to help you out.
If I listen to the demo, I hear 2 obvious things:
- a bandpass filter is being used with resonance
- an LFO is routed to the amplifier is being used with a waveform that's most likely a sine or softened square.
Since you didn't tell us if you have Reason 3 or 4, here's the sound using Subtractor:
I can't tell you what it sounds like or give you the preset, because the demo version restricts exactly those two things. Just copy the settings - it's good to learn how the synth works anyway, and you should have something that gets close to it. Not exactly of course, because the MS2000's filter isn't the same as the one in Subtractor. Since Subtractor is mono and the MS2000 patch has a stereo feel going on, I put a chorus behind it, which is probably good enough.