Proceed with steps outlined in MS KB 325379 However do not use X:\i386 path in step 5 as this will only upgrade schema to version 30 and the server will fail to join domain when running “dcpromoâ€. Instead use second CD directory R2\COMP\ADPREP
The short summary:
dcdiag /e /test:frssysvol
dcdiag /e /test:fsmocheck
repadmin /showreps
adprep /forestprep
adprep /domainprep
After that you are [...]