Serene,
Based on the fact that you are the only one needing access to the second instance of AC, Bert's suggestion of installing a Virtual Machine (VM) onto your machine and run the instance that you need access to on there is an excellent solution.
Your machine will need to be beefer than a minimal desktop to run the VM well, and memory is your friend. a 64bit OS will be of benefit as well.
Another thing to keep in mind is that you now have *two* different DBs to keep backed up.
The upside is that you can cut-paste from the same keyboard between systems as necessary, and you will probably find multiple monitors, or one large 23-26" monitor to be useful for working on both.
