J.,
I am laughing as I read your post. I can so relate to how you feel! My daughter is 23 months and I introduced her to the potty about 3 months ago. Needless to say, we have had many mishaps, and a few successes. My daughter actually has gone number 2 twice on the potty, but no pee pee yet.
I have a quick funny story to make you feel better. It was bath time, I asked my daugher if she wanted to try the potty, she said yes, so up we went (onto the Dora & Boots seat on top of big potty - I have a stand alone potty upstairs also) I waited and waited, and nothing was happening except my toilet getting stuffed with toilet paper my princess was throwing in (she's got that part down perfect!) After a good try, I took her off the potty - off she ran into the sunroom - naked. I went into the kitchen briefly and Uncle Johnny who was over for dinner walked out of the kitchen with me into the sunroom and there greeting us in the middle of the floor was a very large pile of number 2 and my daughter proudly announcing, "Mommy, look, poopy!!" I was mortified at first, and then realized, these are the memories we will never forget and it is small in comparison. Keep on trying - don't feel like a failure - I am convinced there is no magic formula - just keep encouraging and guiding...good luck!