Dude, you need a ballast to power HID bulbs, including high pressure sodium lamps. A ballast controls the flow of current, allowing the lamp to strike, and then maintains the current to keep the bulb properly illuminated and help prevent it from failing catastrophically.
Fluorescent bulb are ballasted, too, and even CFL's but those kinds of ballasts are built into the bulb itself, or in the fixture in the case of T5, T8 and HID lighting fixtures for industrial use (in office buildings, warehouses, outdoor security lights, street and highway lighting).
In the case of high pressure sodium lighting, you would need a ballast capable of igniting 150 watt HPS lamps. In fact, you would need three such ballasts if you wanted to use all three lamps. This would also be a tad inefficient, in terms of luminous efficacy and cooling requirements.
It would be easier for you to just buy a complete HID lighting system as Jimdamick suggested. It would also be more efficient, as 400 and 600 watt HID ballasts have higher luminous efficacy than the lower wattage ballast\lamps. A 400 watt HID ballast and lamp will put out more light than three 150 watt lamps, and it will use less energy (those three 150 ballasts would actually be using over 500 watts!). A single bulb will also be easier to cool; these bulbs produce a significant amount of heat.
For indoor horticulture, you need a ballast, cord\socket set, reflector (hood, fixture housing socket\lamp) and the lamp (bulb) itself. The wattage of the bulb needs to match the wattage of the ballast. The lamp may also need to be the appropriate type of lamp for that ballast, for instance high pressure sodium or metal halide. The cheapest type of ballast available is referred to as a magnetic core\coil. Some of these can ignite both HPS and MH lamps, and feature a switch to enable this.
The newer type of HID ballast is an electronic\digital ballast. Most brands of digital ballast are capable of igniting both types of HID bulbs, and can detect the bulb type automatically. Some of these ballasts also feature a nob that allows you to change the ballast output, so you can dim a bulb or ignite lower wattage lamps. Digital ballasts run completely silent (some do have cooling fans) and slightly cooler. Certain brands can cause interference with radios, speakers and other electronic equipment. The better brands feature RF-shielding to prevent this.
In general, both types of ballasts and corresponding lamps come in a variety of wattages. Bulbs are manufactured and sold specifically for indoor growing, and also come in various other flavors related to the spectral characteristics or color temperature of the bulb. The most common are 250, 400, 600, 800 and 1000 watt lamps.
