Measure AD Performance

Hello,

I???ve been asked to test our AD performance in order to know if it will resist a load of 30% of logons etc.
We have 2 servers Windows 2003 R2 Enterprise

I don???t see in the web any free useful tool, and I dare not to run the ADtest tool directly just in case I crush the machines???
Moreover, I find the tool dificult to me.
Anyone knows any other tool to accomplish the requirement? Any example?

Thank you very much!!
Alberto