I have assisted a few customers in their upgrade to SQL 2005 and generally sent them the following information and I have had a 100% success rate with it so this will be a good starting point
Technotes around SQL 2005:-
1. Make sure that the VSA is a local administrator on all nodes of the cluster
2. Ensure that you create a SQL login for the VSA and that this has at least db_datareader role assigned to all vault related databases. (In my SQL cluster I just created I gave it dbo access to all databases) It also needs the db_creator role for when you need to create databases in the future.
3. What is VERY important is that the SQL 2005 server that you are going to has the same server collation than the SQL server you are coming from. Also check that all of the system databases have the same collation. If not then you will have problems when upgrading next. This is the last technote referenced above.
4. Also when you move the databases ensure the ODBC DSN points to the new SQL server
5. Lastly when you have moved the databases ensure that the compatibility level of your SQL databases are at 90 not 80. This is on the properties of each database in the options section