Backup an enterprise application server and restore What is the best practice to back up a server running Drupal? 
I have backed-up server A, and I want to restore it on server A using server B (both are not on same network). 
On both server I have Windows Server 2008, and for backup I am using "Windows server backup."
I am not sure what you're exactly asking for.

Do you want to do this automatically on a regular basis, or just as a cold/manual standby? We are very happy with Drive Snapshot for full Windows Server backups.
If you're looking for hot failover solution you have to work with redundant machines on all levels (Load Balancer, Web Server, DB Server, File Server). Be prepared to spend some weeks of work (or about 1000 Euros/month) to get this working.
About Drupal 6 itself: You have to backup the DB and the files. For the files the backup &amp; migrate module is very handy. You could combine drush and rsync, but on Windows you will face some problems. Cygwin could solve some of them.