2 databases in sql server 2005 "Production Server" Can 2 databases decrease the performance in a SQL Server 2005 production server?

Server specs:

Dell Power edge 2950, 2 Quad core Xeon, 16 GB of RAM, 3x73 GB SATA hard drive hot plug, Windows Server 2003 R2 Standard Edition 64 bits and SQL Server 2005.

Our accounting/service software company asked me to make a second database "test", basically is a copy of the live database which is 30Gb. I don't have enough disk space on my server. The live database is on a second partition and 42.2 free space. I have setup SQL Server to use a max of 13Gb RAM and lock pages in memory, leave the rest of memory ram to the OS. I'm concern that to have a copy of the live database in the same server will have a high degradation in performance and to start dumping memory.
Having a test database on a production instance sounds like a very bad idea to me, even without taking performance into account.

However, a second database on the instance does not consume resources per-se. It's the user or application activity that drives load to the instance. Obviously, you will need storage to accomodate the data and log files and that could degrade the NTFS performance if the free space on the volumes goes lower than 20%.

Other than that, buffer consumption and CPU/disk/network time depend on activity, not on the database existance alone.