Are you planning on just installing 5.1.9 and using the existing repository? (No upgrade to the repository tables should actually be involved.) Or are you planning on cloning the repository elsewhere?
If you’re just using the existing repository with the new version of software – you’ll need to open each report, and refresh and see if there were any changes due to changes in the calculation engine (which happened in version 5.1.4, I think).
Here’s a past discussion – which has a link to a BusinessObjects support page which discusses the changes, and has an impact analysis tool.
If you’re cloning the repository – you have to be sure that once you generate the BOMain.key for the cloned repository that the VERY FIRST THING that you do is to go into Supervisor and change the connections to all of your universe and document domains, or else your clone security domain will still be pointing to your original universe and document domains, and you’ll get cross-linked repositories.
(Here’s an entry in the Supervisor FAQ that talks about this.)
Anita Craig 
(BOB member since 2002-06-17)