Where to place a new database for new application ?

Hi,

There are a number of SQL server (2008R2 and 2008) running in our site.  There is a new application that uses SQL Server.

My manager doesn't want to purchase SQL Server License and ask where to place the new application.  What should I ask him before answering his question ?  Like the performance / security requirements ?

Besides, it appears that putting databases of different applications in the same SQL Server installation will mess up the configuration.  Is there any suggestion ?

Thanks