OK, a little background for those that are not familiar with Occult Lore: It is a book on additional Magic. All sorts of stuff. I won't get into details on it all. The chapter on Dreams is titled Oneiromancy. It is 27 pages long with both OGC and PI. There are some really good ideas on using dreams in your campaign. On to the specifics...
The base mechanics revolve around the Lucid Dreaming skill. It is untrained and Wisdom based. All characters have Dream Points when they are in a dream. Dreams are just projections and you cannot be permanently killed in dreams. However, if you die in somebody else's dream, you may take subdual damage and temporary Wisdom damage. Combat basically works the same, except you are in a dream and the impossible is suddenly possible right? Enter the Lucid Dreaming skill.
Most classes get a limited number of dream points, 2 + Wis bonus as base, +1 + Wis bonus for every character level above 1st. Monks, Sorcerors and Wizards get twice as many to start, and 2 + Wis bonus per level above 1st. There is also the Oneiromancer PrC that gains 4 + Wis modifier for each level in the PrC. And a character with ranks in the Lucid Dreaming skill gets bonus dream points.
With Dream Points, you can try to alter your dream reality. You can modify the environment, you can give your weapons a greater threat range, you can mimic a skill, feat, or any spell affect, you can change your stats, and you can even modify die rolls. A lot you can do. Take an example of a well trained mage/oneiromancer that, in a dream combat, goes before everyone in the party and strikes out in a whirlwind attack, with his quarterstaff that is larger and has razor blades, knocking all the opponents down in the first round. That might surprise the fighters. Of course, when the tank suddenly starts flying, it might take everyone off guard as well.

Each attempt to do something different in a dream requires a roll of the Lucid Dreaming skill and the expenditure of Dream Points. There are limits as to how many Dream Points you can spend in a round.
Back to the dream world. You can adventure in somebody else's dream. One thing I am contemplating is having the characters adventure in the dream of one of their nemisis'. However, instead of having all their normal equipment, the villian is dreaming about them being trapped in his dungeon, without equipment, etc. Basically, in a bad situation. Then they can try to save themselves. In the process, they would have the chance to learn more about the villian. And if they won, it might really give the villian a shake about his "bad dream".

It could be an interesting scenario. But, I digress. You can adventure in the dreams of just about anything. Obviously, for the dreams to be an interesting component of the game, it should be in the mind of something that has a story hook. Like the mind of the BBEG, or of a forgotten God. There are new magic items and a property called "Transient" that allows magic items to exist in dreams. The item has a different appearance in the dream world and it actually disappears from the real world when the owner begins dreaming. One idea seed is a quest to recover an artifact that is in the Dream World. The party must recover the item in whatever dream prison it is in and then bring it back to the real world. Some neat ideas actually. For combat variance, there are also some templates that you can apply to creatures to make them appropriate dream constructs. Think of a wolf with the Id Manifestation that is even more brutal, and vicious, and tough, than a normal wolf. That sort of thing.
I have basically highlighted the crunchy bits dealing with dreams. There is a lot of flavor text that I find to be good reading. The MSRP is $29.95 for Occult Lore so I would suggest taking a look at one of the reviews to see if the rest sounds useful to you. I won't use everything in the book for my games, but there is certainly enough that I will use that I think it is a good book.
I hope that helps some.