windows 2000 fsmo failover role

In windows 2000 if i have 2 dcs and if the main dc fails ,will the users be able to login using he other dc.What is the concept of standby dc.Are the fsmo roles mainly the pdc,infra and rid master transfeered automatically to the other dc,or do we need to transfer it to the other dc.

I had faced such a prob with an ibm x225 series server ,when it was down due to ram problem.I had made an additional dc ,but the roles weren't trnasferred ,When itried to transfer the roles from the ibm server to additional dc ,it gave me an error as the server is offline.


kindly help.