Notebook computer with combined headphone/mic jack: Can I use mic + speakers?

Hi, I’m looking to purchase a notebook computer for a teaching lab. Our IT department recommends a Dell computer that has a combined microphone/headphone jack. The computer will run Windows 7 Home Premium.

I’ve never used a computer with such a jack, but I assume that the default behavior is to shut off the built-in speakers when something is plugged into the jack. Problem is, my application requires me to plug in a microphone and listen to the sound over speakers.

My question: With such a computer, can I plug in a microphone and play sound through the speakers? Does it depend on the specific driver I happen to have, or is this always an option on such a computer? Is it something I can set in the Control Panel “Sound” settings?

What is the model number for the computer? It would be useful to see what the manual has to say about how to use both an external microphone and external speakers.