Exchange 2010 install within an Exchange 2003 forest

I am installing exchange 2010 inside an organization which exchange 2003 already exists.

I ready the following article:

http://social.technet.microsoft.com/forums/en-us/exchangesvrmigration/thread/BA1BE8A1-19DD-48E6-B6D2-2A619108E2D8

Which says to remove ADC components.

My question is when this is removed how does exchange 2003 function with Active directory since the components were removed?

Thanks,

Richard