Make sure none of the scripts use tables with the same names. Or if they do that all of the scripts can survive using the same table. i.e. if they all access a table called users, can you combine them all into 1 table? This would require making sure that all the fields used by each script appear in the table, and that they are all populated correctly, and that any extra fields won't corrupt or get corrupted by the other scripts.
If you can't combine all of the same named tables can you modify the names of the tables in each script? And will this have any adverse affect on your site as a whole? i.e. users haveing to create multiple accounts and the like. If you can rename the tables in the scripts then you just need to create the tables with the new names in a single database and modify each script to access this database instead of the one it was previously accessing.
This isn't an easy task, but it also shouldn't be impossible.
