SQL Server is required to install backup exec 10. there isn't a way around this. You do have the choice however if you want to install MSDE (Microsoft SQL 2000 Desktop Engine) or add it to an existing SQL database on the network. We installed it to an existing SQL server without problems. Make sure that SQL 2000 server is Service Pack 3a.
Not sure if SQL 2005 is usable yet maybe in a future patch
apart from logs, which are in xml, the sql database part of BE is important and stores relevant data to run BE.
You cant disable the SQL.