Hi S.!
I have a 5 yr old boy and a 2 yr old. I tried each and every one of the suggested things from the others and none of them worked for him. He was VERY interested at 19 months but like one of the other moms said, he lost interest as soon as we started "encouraging" him. I gave up and let him lead the way, then when he approached 21/2 I started trying again only to end up with wet pants which he didn't seem to mind for some awful reason. :)(My girlfriends told me to just let him wet his pants and he would realize he doesn't like the feeling, didn't work). My boy LOVES movies and I don't let him watch much TV at all so one day I suggested that if he could stay dry all day, he would get a movie that evening, that did it! by the end of the week he was dry and had maybe 2 accidents that year. He also stayed dry through the night, I am not sure how I go so lucky with that but now we are patiently waiting for our 2 yr old boy to tell us he is ready, which is not happening, but he is a different kid.
Oh, also, we did the sit down thing too, MUCH cleaner, almost wish we still did it! Once he mastered that (and I am talking months) we started talking about standing and he tried both for a while, then went to standing. We tried little spongy things that went in the toilet for aiming, it was too much I think to try to stand, aim (without freaking mom out with you know what on the ceiling) and peeing all at the same time. :)
Be patient. My son was 3 yrs old when he successfully went on the toilet consistently.
W., Mom of Zach(5)and Camden(2)