Additional domain controller in 2008 r2 standard

I have domain controller installed on windows 2008 32 bit sp2 , now i want to add additional domain controller on  windows 2008 R2 SP1 .

Is it possible ? . If yes is there any negative impact ? . Do i need to run adprep /forestprep  again on the existing domain (windows  2008 32 bit ) or  on windows 2008 r2. 

What all i need to care about before or after installation 

Thanks