What is the difference between George and Lennie's dream, compared to Curley's wife's dream?
In Of Mice and Men, there really is no difference between George and Lennie's dream and Curley's wife's dream: both are ideas that keep these characters going, but have no realistic chance at actually occurring.
In the novel, George and Lennie have a shared dream of buying a small ranch and "live off the fatta the lan'." While Curley's wife has the dream of being in movies "an' had nice clothes—all them nice clothes like they wear. An' I coulda sat in them big hotels, an' had pitchers took of me."
Steinbeck makes sure readers see the connection because he juxtaposes the telling of Curley's wife's dream with Lennie telling his and George's dream in Chapter 4. In this chapter, Curley's wife gets angry at Lennie for not listening to her story about how she ended up on the ranch and missed out on her dream of being in the movies. But after telling Lennie her entire story (her mom and then Curley prevented her from following her dreams), Lennie shows little interest. Instead, he discusses how he won't be able to "tend the rabbits" if George finds out about the dog Lennie had just killed. He then goes on to tell Curley's wife about the "house an' a garden and a place for alfalfa, an' that alfalfa is for the rabbits..."
Curley's wife's dream is literally ended a few pages later when Lennie accidentally snaps her neck. Lennie and George's dream is literally ended when George shoots Lennie in the back of the head in the next chapter.