how to make this lead?

does anyone know how to make this lead? i recently heard it in "wilkinson - need to know" and immediately recognized that lead sound from a song that was a big guilty pleasure of mine back in the day - "kreo - burn for you". my guess is that this sound might be square wave-based and is monophonic with a fair amount of portamento but i can't get the tonality right so there's definitely something else to it. it's such an infectious sound.

the sound is at 0:00 in the song below:
http://www.youtube.com/watch?v=-PoX1cPgCRg

the sound starts at 0:45 in the song below:
http://www.youtube.com/watch?v=bp9xdVV6uxQ

thanks for the help. i wasn't able to get very close with ES2 but here's as close as i could get with the old Virus TI. 2 square waves, one is -12 and the other is +19 plus some detune, unison, unison detune, some virus fx and some very mild lfo-based pitch modulation. i just whipped up a random melody so it's kind of hard to compare to the ones above because of that.

https://soundcloud.com/djdizzyofficial/test-lead/s-n93Tg

wow, thanks