DB2: Reinstall doesn’t complete successfully

Problem:

DB2 re-installation on same machine ends with error that it can’t set variable DB2INSTANCE.

Resolution:

1. Remove directory db2admin from folder “C:\Documents and Settings”. If you get an error related to folder is being used that means there is still a DB2 process running. In such case, you will need to use regedit to cleanup the service entry and restart. Then try to delete the directory again.
2. User computer management to delete db2admin user and groups DB2USERS & DB2ADMNS 

 Important:
The steps above are not intended for production boxes but for a developer's machine only.