Hi Naveen,
But if you have ND you will take the advantage of the clustering, making a cluster between two physical/virtual box if one of your machines goes down then other continue with the service.
Take a look to next redbooks:
WebSphere Application Server Network Deployment V6: High Availability Solutions
www.redbooks.ibm.com/abstracts/sg246688.... WebSphere Application Server V6 Scalability and Performance Handbook
www.redbooks.ibm.com/abstracts/sg246392.... Then you need to review new features of WAS v8.5 (dinamic clustering, ODR,...) that give more functionality than in version 6.1
If you want only to recover one physical box my suggestion is take a backupconfig of WAS profile(s).
Install new physical/virtual machine with same name, install WAS in same directory and restore the profile(s).
Hope this helps.
regards