Three sticks or two?

I currently have 2x 256 mb sticks, and I want to upgrade to 1GB. I have heard that I can run three sticks in Dual channel, but I am not sure if it would run the same as two sticks.

So my question is would it be better to buy one stick of 512 or dump the two I have and buy 2x512? Also does it help to buy the same type of ram that I already have? Use small words please, I know less than nothing when it comes to ram.

it might now run the same because the 2 packs of dual channle are set at an exact speed..........it will be much faster than single channle but not as fast as 2 dual channle, id bet.