Windows 2003 to Windows 2003 r2 upgrade

I have a single forest w/ two sites east and west. All the DC’s in the west are win2k3 r2, the servers in the east are win2k3 sp1. I need to up grade my DC’s (east site) to R2 in order to support Identity Management services for Unix. My question is this;

Do I need to run the adprep /forestprep on both of my DC’s or is one enough?…or is there no need as my West DC have done this already?

I assume I will need to run adprep /forestprep
on both my DC’s (east) in order to support the added features R2 has…just want to be 100%.

Thx in advance,
MK