Hope your closets aren't the type that crease at the center, and slide along rails.. very frustrating to completely lightproof!
You say your closet is 3.5 * 5.6 feet? So that's 19.6 square feet.
The general rule of thumb is 3000 - 5000 lumen per square foot. So that's 58,800 - 98,000 lumen to cover your closet.
I would recommend using a 400 watt hps (puts out 50,000 lumen), and a 400 watt mh (puts out 36,000 lumen). This would give you a nice mixed spectrum, and you'd have plenty of light for a good yield.
This is where it gets tricky though, because your room isn't a square, the lights will be harder to position. Some areas of the room are going to get more light than others. "I" would mount these in the corners of the closet, and have them pointing at a slight angle, so that they both cover the room.
Hopefully some others will weigh in and make a suggestion, I'd be interested to know what others would do.
If anyone cares, I'm referring to these charts for lumen output of bulbs:
http://www.marijuanapassion.com/forum/attachment.php?attachmentid=6265&d=1149604828
http://www.marijuanapassion.com/forum/attachment.php?attachmentid=6266&d=1149604828
edit: Woops, for only 4 or 5 plants, a 400 watt HPS should work fine on it's own.