If you're just starting out in Omaha, you probably want to start out with fixed limit Omaha Hi. It's harder to find a game but there is usually at least one going at the PokerStars
microlimits, but the mistakes you can make by jumping straight into PLO can be very expensive (trust me, I know). Also, I would recommend "Farha on Omaha". It has 3 chapters: one on Omaha hi fixed limit, one on pot limit Omaha hi, and another on limit Omaha hi/lo. It's not much in the way of starting hand charts or clear-cut examples, but it does have some useful information, especially for the beginning Omaha player.