NT registry file problems

Hi
The other day, I was installing Norton Antivirus 2000 on an NT 4.0 workstation( srv pack 4) and after a while the machine crashed . When I restarted the machine , it would boot up ok, but would not load anything after initial login. ( and of course I did not have the lastest emergency repair disk !!!)

I suspected the registry , so I tried to remotely connect to the registry from another machine.. it would not let me make changes to it as it was in use.

The question I have , is there any utility/program I can use to modify the registry in the case ? Is there any way of recovering from major registry problems in case , you miss make a backup copy of the registry?