1) Install SQL 2005 SP3 explicitly on your Backup Exec server. While installing SQL uncheck ” Hide advanced configuration option”
2) During installation you will get an option to give a name to the SQL instance, name it as “BKUPEXEC2010″
3) Once the installation completes successfully, check if the SQL service with the name as ” SQL Server BKUPEXEC2010″ is listed in windows services console. If the service is started then proceed with the next step
4) Move the BE database from the existing SQL instance to the new SQL instance, refer to http://support.veritas.com/docs/351948
5) Once the database is moved to the new instance, run the installation of BE2010.
6) In the installation wizard you will not see the SQL installation as we have already installed it manually.
Refer to http://support.veritas.com/docs/312651, not sure if it works in case of BE2010 as its applicable to BE12.5.