did you go to the advanced science talk, or where u part of the tsp thing they had? i thinke basically, if you've managed to make olympiad stage, or if you get a uai of above 98.8 (though this may change for our year), or if you do really well in a science subject or 4u maths, then on your uac offers sheet, it will say whether u have been offered to take part in tsp or not. if you dont get that, you can always contact the faculty and present your case eg. if you're doing a double degree, make sure you list it as sci/eng for example, rather than eng/sci - apparantely this caused alot of problems last year.
having said that, i was part of the tsp thing held in the morning (the free lunch was yum), but it didn't really appeal to me that much - prbly cos im not really a science type of person, more commerce.