You might look through the archives in cardplayer.com under writers. I know Cappelletti has some Omaha articles there. Clonie Gowen wrote an excellent Omaha article, believe it or not. It might be in those archives or you can google Clonie Gowen omaha and find it. It really helped my game. I think it might help answer your question. In Omaha, if your hand can't improve, it sucks against players who refuse to drop their strong draws. May also check out [url=http://www.pot-limit-omaha.com/]http://www.pot-limit-omaha.com/[/url] for some very basic stuff.
I wouldn't recommend buying a book. Find Capetelli's starting hand requirements and just play. You'll figure it out as you go. Check a few sites and read some articles.
Found this list that is good to have:
Pot-Limit Omaha: Top Advice
1. Be very selective with your starting hands: nothing is more important than choosing the correct starting hand for a certain situation.
2. Table selection: only play in games where you have an edge. You want at least a couple of weak players at the table when you sit down.
3. "Play the players": be sure to quickly assess the opposition: who plays inferior hands, who folds at aggression, who bets with draws, who calls big bets with weak hands and draws, who can be bluffed, who bluffs, etc.
4. "Pump it or dump it": fold or bet/raise (if the odds are with you). You should avoid calling unless you have a good reason (such as trapping an opponent or increasing your pot odds when you are on a big draw).
5. Respect most big bets and raises: this is particularly true in Pot-Limit Omaha since most players do not bluff.
6. Do not get "married" to the nut flush draw: the difference between drawing to the nut flush in Omaha as compared to Hold'em is that in Hold'em you can usually win the pot by pairing your Ace or win the pot with a flush even though the board pairs. The same is not true in Omaha.
7. Do not get "married" to an eight way straight draw: in Omaha, it is possible to flop 13-way, 17-way and 20-way straight draws. It is best to wait until you hold one of these draws before you heavily involve yourself in the pot.
8. Do not overplay unsuited Aces: when all you hold are a pair of Aces and two unsuited, unconnected rags, there is little you can flop to improve your hand. If you do not flop an Ace, you will usually end up with a weak holding.
9. Bet your best drawing hands: enhance the deception in your game by betting your strong draws, as you will also win more pots without a fight.
10. Always draw to the nuts in multi-way pots: when all the money goes into the middle in multi-way pots, be sure to draw to the nuts. Avoid committing all your money with draws without additional value as you can find yourself trapped between a set and the nut flush draw, maybe leaving you with only a nut straight draw that might end up in a split pot if you hit.

Where i found OMAHA book. any site for free download?