You can stick with the 23w CFL's if you can't afford the 42watt bulbs. The 42 watt bulbs give you about 1000 or so lumens more. Honestly, it depends on the size of your space. Most important thing to remember is LUMENS are more important than WATTAGE. 23w = 1600 (or 1750) Lumens. I say OR 1750 because it depends on the brand of 23watt you are buying. It should tell you the lumens and spectrum right on the package. You can take the different brands and compare them side by side and go with the higher LUMENS. 42 Watt CFL's give off 2700 Lumens and are equal to 150watts. You need about 2000 lumens per square foot. Just measure your space and do the math. Figure out how many LUMENS you need. Your spectrum is right on for veg. 6500K. When you are ready to flower you can switch to the "Soft White" CFL's. They are in the 2700K part of the spectrum. Basically, the red, yellow, and amber you need for flowering. You can buy these CFL's anywhere... Wal-Mart, K-Mart, Lowes, Home Depot, etc... Just make sure your entire plant is covered at all times. Add more as it grows or as you can afford more.
5 6500K CFL's (23w or 42w -- obviously 42w will give you more lumens) are equal to One MH lamp
5 2700K CFL's are equal to One HPS Lamp.
I've read that in many places...