ssscientist is right, I actually achieved very close results last night using RGC triangle II (Really the swiss army knife of freeware!!!).
Using the first preset I just set both oscillators to square, turned the portamento to about the 9 o'clock position, increased the attack time ever so slightly, and swept the filter settings around to taste.
The trick to this sound is in how it is played (definitely easier if you are using a realtime controller). In order to get the slurring parts to play right you have to depress the first key of the part (Play Mono), and while holding it down press and release the next key (which in effect gives you 2 notes per additional key press/release but without retriggering the sound). Then for the quick notes, your just playing the keyboard as normal. This song uses both styles to good use.
If you do not have a realtime controller, and are step editing, it is a matter of drawing the First note the length of the measure (or however long you need), and then drawing in notes above or below this one where there is to be new notes. Just be sure that the first note spans the length of the run, otherwise the preset will retrigger all the EG's, and you will lose the fluid sounding transitions of the notes in the part your trying to write.
Hope this helps, and I didn't confuse you too much, I can do things pretty good usually, but when comes to teaching, I suck....I really lack patience, that's the problem. But if you get stumped let us know. Myself, or someone else can eventually get you through this.
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