One more question!
-what is the significance of the conversation between adam and the cowboy in which the cowboy states that if he appears to adam twice more than Adam has done something bad, and if only once more than Adam has done the right thing?

We see the cowboy twice more in the movie although only once more in Diane's fantasy when he is telling her to wake up.

I agree that it makes sense that the cowboy was a guest at the party that she incorporated into her dream, but I can't figure out what the see me once/twice thing is all about.

I really loved the use of the Cowboy in this movie. Such a character based on nothing except for his look, his attitude... and a perfect way to use him, as well... when he said, "if you do things right, you'll see me once, if you do things wrong, you'll see me twice", I kept it in my head, and spotted him twice, meaning to me, that the director did things wrong, as in, not choosing the right actress...
When me and my friends finnished this movie, I brought up this point, 2/3s of us saw the cowboy twice, and the rest saw him once. What this means to me is that the cowboy was strictly for us, as the veiwer, but the question is, what is it that 1/3 of us are doing right, and 2/3s doing wrong?

When the cowboy appears for the first time to meet Adam the lamp on the front door of the fence is turning on when he arrives and then turn off when he’s gone. So the cowboy is what we call luciferous , so in my opinion at this particular scene (at least) the cowboy is Lucifer (aka Satan,Evil,etc). Moreover above the lamp is goat’s skull a classic symbol of satan.

I just wanted to say bingo! The devil theory is where I am at right now. There is something there we are all missing. I can't put my finger on it but I am close. But I do agree that the cowboy is the devil, and maybe he woke Diane from the dead and not her sleep. Perhaps the first part of the movie was real and Diane sold her soul to get that life, took her deal with the devil away, so he awoke her back to her other life. That made no sence I know. Sorry!

We see him (at least?) three times in all: 1) at the corral, 2) as he wakes up Diane, 3) at the pool party.
I say he was only seen one more time by the person to whom it mattered: Adam.
Now, you'll have to hear my long theory on the Cowboy. I belive the first part of the movie was a dream, Diane's dream of what it should have been like. Her dream does many things, including explaining why she didn't get the part. In her dream, she loses the part to Camilla due to this vast conspiracy, where the cowboy forces Adam to pick her. Now, let's flash to the dinner scene. Notice how Diane looks around and sees (the guy played by Angelo Badalamenti) and the mysterious cowboy walking outside. IMO, these are just two absolutely trivial characters in reality. However, she subconsciously latches onto them and uses them in her dream, making the whole conspiracy idea. So, his appearance is explained by Diane's dream. She sees him at the dinner party because he Adam actually did do right. Adam sees him only once. However, we see him twice more after his warning to Adam in the dream. Why? Perhaps to signify that Diane did wrong, or perhaps because he is the ring-leader in the dreamt up conspiracy and thus has the power to wake Diane from her dream.

Thanks this helps a lot-I don't know if I totally understand the explanation of all of the devil stuff. But still Adam does not see the cowboy at all again in the dream b/c he does not see the cowboy when he is waking diane up-and the dinner party is reality.

If cowboy is satan it might explain why the director's name is adam.