In theory, if you are running SQL Server 2000 or higher on Windows 2003 Server with a VSS enabled Bacula client, you should be able to safely back up the live database files.
This is not known to be tested and verified at this time, however, so the recommended solution is to use SQL Servers built in backup facility to dump the database contents to a file which bacula can then safely read. In order to do so, you will need to arrange a 'Client Run Before Job' script that will execute a SQL command like
BACKUP DATABASE yourdb TO DISK='C:\temp\yourdb.bak' WITH INIT
for each database you are backing up. You would then later restore the file with a SQL command like
RESTORE DATABASE yourdb FROM DISK='C:\temp\yourdb.bak'
Make sure you consult the documentation for your version of SQL Server to ensure you are using the right commands, and to back up any other database information you require such as transaction logs.
For more information on backing up SQL Server 2000, go to http://www.microsoft.com/technet/prodtechnol/sql/2000/maintain/sqlbackuprest.mspx