How to pay taxes when you're employed and freelancing?

Hello all! I tried to ask this earlier, but just wanted to rephrase things a bit. I'm currently employed, but am also doing some freelance writing on the side with no taxes taken out. I filled out form 1040-ES which told me I need not make estimated payments at all, because the amount was less than $1,000. Does this mean I don't need to make any quarterly payments on my freelance work at all during 2010? Or do I just multiply my estimated freelance income for 2010 by .153 and pay that amount in quarters to the government? All in all between the two, the AGI will be less than 30,000. Thanks!